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@ -1,784 +0,0 @@
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commit 280858b0bb3384b9ec06b455e196b453888bd6b8
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Author: Tejun Heo <tj@kernel.org>
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Date: Fri Mar 11 07:31:23 2016 -0500
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sched: Misc preps for cgroup unified hierarchy interface
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Make the following changes in preparation for the cpu controller
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interface implementation for the unified hierarchy. This patch
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doesn't cause any functional differences.
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* s/cpu_stats_show()/cpu_cfs_stats_show()/
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* s/cpu_files/cpu_legacy_files/
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* Separate out cpuacct_stats_read() from cpuacct_stats_show(). While
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at it, make the @val array u64 for consistency.
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Signed-off-by: Tejun Heo <tj@kernel.org>
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Cc: Ingo Molnar <mingo@redhat.com>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Li Zefan <lizefan@huawei.com>
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Cc: Johannes Weiner <hannes@cmpxchg.org>
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diff --git a/kernel/sched/core.c b/kernel/sched/core.c
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index 154fd689fe02..57472485b79c 100644
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -8705,7 +8705,7 @@ static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
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return ret;
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}
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-static int cpu_stats_show(struct seq_file *sf, void *v)
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+static int cpu_cfs_stats_show(struct seq_file *sf, void *v)
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{
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struct task_group *tg = css_tg(seq_css(sf));
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struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
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@@ -8745,7 +8745,7 @@ static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
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}
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#endif /* CONFIG_RT_GROUP_SCHED */
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-static struct cftype cpu_files[] = {
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+static struct cftype cpu_legacy_files[] = {
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#ifdef CONFIG_FAIR_GROUP_SCHED
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{
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.name = "shares",
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@@ -8766,7 +8766,7 @@ static struct cftype cpu_files[] = {
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},
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{
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.name = "stat",
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- .seq_show = cpu_stats_show,
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+ .seq_show = cpu_cfs_stats_show,
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},
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#endif
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#ifdef CONFIG_RT_GROUP_SCHED
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@@ -8791,7 +8791,7 @@ struct cgroup_subsys cpu_cgrp_subsys = {
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.fork = cpu_cgroup_fork,
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.can_attach = cpu_cgroup_can_attach,
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.attach = cpu_cgroup_attach,
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- .legacy_cftypes = cpu_files,
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+ .legacy_cftypes = cpu_legacy_files,
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.early_init = true,
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};
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diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
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index bc0b309c3f19..d1e5dd0b3a64 100644
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--- a/kernel/sched/cpuacct.c
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+++ b/kernel/sched/cpuacct.c
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@@ -276,26 +276,33 @@ static int cpuacct_all_seq_show(struct seq_file *m, void *V)
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return 0;
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}
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-static int cpuacct_stats_show(struct seq_file *sf, void *v)
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+static void cpuacct_stats_read(struct cpuacct *ca,
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+ u64 (*val)[CPUACCT_STAT_NSTATS])
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{
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- struct cpuacct *ca = css_ca(seq_css(sf));
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- s64 val[CPUACCT_STAT_NSTATS];
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int cpu;
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- int stat;
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- memset(val, 0, sizeof(val));
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+ memset(val, 0, sizeof(*val));
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+
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for_each_possible_cpu(cpu) {
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u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
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- val[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
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- val[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
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- val[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_SYSTEM];
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- val[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_IRQ];
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- val[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_SOFTIRQ];
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+ (*val)[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
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+ (*val)[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
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+ (*val)[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_SYSTEM];
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+ (*val)[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_IRQ];
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+ (*val)[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_SOFTIRQ];
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}
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+}
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+
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+static int cpuacct_stats_show(struct seq_file *sf, void *v)
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+{
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+ u64 val[CPUACCT_STAT_NSTATS];
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+ int stat;
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+
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+ cpuacct_stats_read(css_ca(seq_css(sf)), &val);
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for (stat = 0; stat < CPUACCT_STAT_NSTATS; stat++) {
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- seq_printf(sf, "%s %lld\n",
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+ seq_printf(sf, "%s %llu\n",
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cpuacct_stat_desc[stat],
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cputime64_to_clock_t(val[stat]));
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}
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commit 015cbdcb90034fd566d00de9d3d405613da3cd26
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Author: Tejun Heo <tj@kernel.org>
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Date: Fri Mar 11 07:31:23 2016 -0500
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sched: Implement interface for cgroup unified hierarchy
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While the cpu controller doesn't have any functional problems, there
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are a couple interface issues which can be addressed in the v2
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interface.
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* cpuacct being a separate controller. This separation is artificial
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and rather pointless as demonstrated by most use cases co-mounting
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the two controllers. It also forces certain information to be
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accounted twice.
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* Use of different time units. Writable control knobs use
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microseconds, some stat fields use nanoseconds while other cpuacct
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stat fields use centiseconds.
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* Control knobs which can't be used in the root cgroup still show up
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in the root.
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* Control knob names and semantics aren't consistent with other
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controllers.
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This patchset implements cpu controller's interface on the unified
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hierarchy which adheres to the controller file conventions described
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in Documentation/cgroups/unified-hierarchy.txt. Overall, the
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following changes are made.
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* cpuacct is implictly enabled and disabled by cpu and its information
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is reported through "cpu.stat" which now uses microseconds for all
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time durations. All time duration fields now have "_usec" appended
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to them for clarity. While this doesn't solve the double accounting
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immediately, once majority of users switch to v2, cpu can directly
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account and report the relevant stats and cpuacct can be disabled on
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the unified hierarchy.
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Note that cpuacct.usage_percpu is currently not included in
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"cpu.stat". If this information is actually called for, it can be
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added later.
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* "cpu.shares" is replaced with "cpu.weight" and operates on the
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standard scale defined by CGROUP_WEIGHT_MIN/DFL/MAX (1, 100, 10000).
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The weight is scaled to scheduler weight so that 100 maps to 1024
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and the ratio relationship is preserved - if weight is W and its
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scaled value is S, W / 100 == S / 1024. While the mapped range is a
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bit smaller than the orignal scheduler weight range, the dead zones
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on both sides are relatively small and covers wider range than the
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nice value mappings. This file doesn't make sense in the root
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cgroup and isn't create on root.
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* "cpu.cfs_quota_us" and "cpu.cfs_period_us" are replaced by "cpu.max"
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which contains both quota and period.
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* "cpu.rt_runtime_us" and "cpu.rt_period_us" are replaced by
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"cpu.rt.max" which contains both runtime and period.
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v2: cpu_stats_show() was incorrectly using CONFIG_FAIR_GROUP_SCHED for
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CFS bandwidth stats and also using raw division for u64. Use
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CONFIG_CFS_BANDWITH and do_div() instead.
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The semantics of "cpu.rt.max" is not fully decided yet. Dropped
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for now.
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Signed-off-by: Tejun Heo <tj@kernel.org>
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Cc: Ingo Molnar <mingo@redhat.com>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Li Zefan <lizefan@huawei.com>
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Cc: Johannes Weiner <hannes@cmpxchg.org>
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diff --git a/kernel/sched/core.c b/kernel/sched/core.c
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index 57472485b79c..c0ae869f51c4 100644
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -8784,6 +8784,139 @@ static struct cftype cpu_legacy_files[] = {
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{ } /* terminate */
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};
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+static int cpu_stats_show(struct seq_file *sf, void *v)
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+{
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+ cpuacct_cpu_stats_show(sf);
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+
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+#ifdef CONFIG_CFS_BANDWIDTH
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+ {
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+ struct task_group *tg = css_tg(seq_css(sf));
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+ struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
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+ u64 throttled_usec;
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+
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+ throttled_usec = cfs_b->throttled_time;
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+ do_div(throttled_usec, NSEC_PER_USEC);
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+
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+ seq_printf(sf, "nr_periods %d\n"
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+ "nr_throttled %d\n"
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+ "throttled_usec %llu\n",
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+ cfs_b->nr_periods, cfs_b->nr_throttled,
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+ throttled_usec);
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+ }
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+#endif
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+ return 0;
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+}
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+
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+#ifdef CONFIG_FAIR_GROUP_SCHED
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+static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
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+ struct cftype *cft)
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+{
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+ struct task_group *tg = css_tg(css);
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+ u64 weight = scale_load_down(tg->shares);
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+
|
|
|
|
|
|
|
|
+ return DIV_ROUND_CLOSEST_ULL(weight * CGROUP_WEIGHT_DFL, 1024);
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
|
|
|
|
|
|
|
|
+ struct cftype *cftype, u64 weight)
|
|
|
|
|
|
|
|
+{
|
|
|
|
|
|
|
|
+ /*
|
|
|
|
|
|
|
|
+ * cgroup weight knobs should use the common MIN, DFL and MAX
|
|
|
|
|
|
|
|
+ * values which are 1, 100 and 10000 respectively. While it loses
|
|
|
|
|
|
|
|
+ * a bit of range on both ends, it maps pretty well onto the shares
|
|
|
|
|
|
|
|
+ * value used by scheduler and the round-trip conversions preserve
|
|
|
|
|
|
|
|
+ * the original value over the entire range.
|
|
|
|
|
|
|
|
+ */
|
|
|
|
|
|
|
|
+ if (weight < CGROUP_WEIGHT_MIN || weight > CGROUP_WEIGHT_MAX)
|
|
|
|
|
|
|
|
+ return -ERANGE;
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ weight = DIV_ROUND_CLOSEST_ULL(weight * 1024, CGROUP_WEIGHT_DFL);
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ return sched_group_set_shares(css_tg(css), scale_load(weight));
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+#endif
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+static void __maybe_unused cpu_period_quota_print(struct seq_file *sf,
|
|
|
|
|
|
|
|
+ long period, long quota)
|
|
|
|
|
|
|
|
+{
|
|
|
|
|
|
|
|
+ if (quota < 0)
|
|
|
|
|
|
|
|
+ seq_puts(sf, "max");
|
|
|
|
|
|
|
|
+ else
|
|
|
|
|
|
|
|
+ seq_printf(sf, "%ld", quota);
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ seq_printf(sf, " %ld\n", period);
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+/* caller should put the current value in *@periodp before calling */
|
|
|
|
|
|
|
|
+static int __maybe_unused cpu_period_quota_parse(char *buf,
|
|
|
|
|
|
|
|
+ u64 *periodp, u64 *quotap)
|
|
|
|
|
|
|
|
+{
|
|
|
|
|
|
|
|
+ char tok[21]; /* U64_MAX */
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ if (!sscanf(buf, "%s %llu", tok, periodp))
|
|
|
|
|
|
|
|
+ return -EINVAL;
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ *periodp *= NSEC_PER_USEC;
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ if (sscanf(tok, "%llu", quotap))
|
|
|
|
|
|
|
|
+ *quotap *= NSEC_PER_USEC;
|
|
|
|
|
|
|
|
+ else if (!strcmp(tok, "max"))
|
|
|
|
|
|
|
|
+ *quotap = RUNTIME_INF;
|
|
|
|
|
|
|
|
+ else
|
|
|
|
|
|
|
|
+ return -EINVAL;
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ return 0;
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+#ifdef CONFIG_CFS_BANDWIDTH
|
|
|
|
|
|
|
|
+static int cpu_max_show(struct seq_file *sf, void *v)
|
|
|
|
|
|
|
|
+{
|
|
|
|
|
|
|
|
+ struct task_group *tg = css_tg(seq_css(sf));
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ cpu_period_quota_print(sf, tg_get_cfs_period(tg), tg_get_cfs_quota(tg));
|
|
|
|
|
|
|
|
+ return 0;
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+static ssize_t cpu_max_write(struct kernfs_open_file *of,
|
|
|
|
|
|
|
|
+ char *buf, size_t nbytes, loff_t off)
|
|
|
|
|
|
|
|
+{
|
|
|
|
|
|
|
|
+ struct task_group *tg = css_tg(of_css(of));
|
|
|
|
|
|
|
|
+ u64 period = tg_get_cfs_period(tg);
|
|
|
|
|
|
|
|
+ u64 quota;
|
|
|
|
|
|
|
|
+ int ret;
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ ret = cpu_period_quota_parse(buf, &period, "a);
|
|
|
|
|
|
|
|
+ if (!ret)
|
|
|
|
|
|
|
|
+ ret = tg_set_cfs_bandwidth(tg, period, quota);
|
|
|
|
|
|
|
|
+ return ret ?: nbytes;
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+#endif
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+static struct cftype cpu_files[] = {
|
|
|
|
|
|
|
|
+ {
|
|
|
|
|
|
|
|
+ .name = "stat",
|
|
|
|
|
|
|
|
+ .flags = CFTYPE_NOT_ON_ROOT,
|
|
|
|
|
|
|
|
+ .seq_show = cpu_stats_show,
|
|
|
|
|
|
|
|
+ },
|
|
|
|
|
|
|
|
+#ifdef CONFIG_FAIR_GROUP_SCHED
|
|
|
|
|
|
|
|
+ {
|
|
|
|
|
|
|
|
+ .name = "weight",
|
|
|
|
|
|
|
|
+ .flags = CFTYPE_NOT_ON_ROOT,
|
|
|
|
|
|
|
|
+ .read_u64 = cpu_weight_read_u64,
|
|
|
|
|
|
|
|
+ .write_u64 = cpu_weight_write_u64,
|
|
|
|
|
|
|
|
+ },
|
|
|
|
|
|
|
|
+#endif
|
|
|
|
|
|
|
|
+#ifdef CONFIG_CFS_BANDWIDTH
|
|
|
|
|
|
|
|
+ {
|
|
|
|
|
|
|
|
+ .name = "max",
|
|
|
|
|
|
|
|
+ .flags = CFTYPE_NOT_ON_ROOT,
|
|
|
|
|
|
|
|
+ .seq_show = cpu_max_show,
|
|
|
|
|
|
|
|
+ .write = cpu_max_write,
|
|
|
|
|
|
|
|
+ },
|
|
|
|
|
|
|
|
+#endif
|
|
|
|
|
|
|
|
+ { } /* terminate */
|
|
|
|
|
|
|
|
+};
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
struct cgroup_subsys cpu_cgrp_subsys = {
|
|
|
|
|
|
|
|
.css_alloc = cpu_cgroup_css_alloc,
|
|
|
|
|
|
|
|
.css_released = cpu_cgroup_css_released,
|
|
|
|
|
|
|
|
@@ -8792,7 +8925,15 @@ struct cgroup_subsys cpu_cgrp_subsys = {
|
|
|
|
|
|
|
|
.can_attach = cpu_cgroup_can_attach,
|
|
|
|
|
|
|
|
.attach = cpu_cgroup_attach,
|
|
|
|
|
|
|
|
.legacy_cftypes = cpu_legacy_files,
|
|
|
|
|
|
|
|
+ .dfl_cftypes = cpu_files,
|
|
|
|
|
|
|
|
.early_init = true,
|
|
|
|
|
|
|
|
+#ifdef CONFIG_CGROUP_CPUACCT
|
|
|
|
|
|
|
|
+ /*
|
|
|
|
|
|
|
|
+ * cpuacct is enabled together with cpu on the unified hierarchy
|
|
|
|
|
|
|
|
+ * and its stats are reported through "cpu.stat".
|
|
|
|
|
|
|
|
+ */
|
|
|
|
|
|
|
|
+ .depends_on = 1 << cpuacct_cgrp_id,
|
|
|
|
|
|
|
|
+#endif
|
|
|
|
|
|
|
|
};
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
#endif /* CONFIG_CGROUP_SCHED */
|
|
|
|
|
|
|
|
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
|
|
|
|
|
|
|
|
index d1e5dd0b3a64..57f390514c39 100644
|
|
|
|
|
|
|
|
--- a/kernel/sched/cpuacct.c
|
|
|
|
|
|
|
|
+++ b/kernel/sched/cpuacct.c
|
|
|
|
|
|
|
|
@@ -347,6 +347,31 @@ static struct cftype files[] = {
|
|
|
|
|
|
|
|
{ } /* terminate */
|
|
|
|
|
|
|
|
};
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
+/* used to print cpuacct stats in cpu.stat on the unified hierarchy */
|
|
|
|
|
|
|
|
+void cpuacct_cpu_stats_show(struct seq_file *sf)
|
|
|
|
|
|
|
|
+{
|
|
|
|
|
|
|
|
+ struct cgroup_subsys_state *css;
|
|
|
|
|
|
|
|
+ u64 usage, val[CPUACCT_STAT_NSTATS];
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ css = cgroup_get_e_css(seq_css(sf)->cgroup, &cpuacct_cgrp_subsys);
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ usage = cpuusage_read(css, seq_cft(sf));
|
|
|
|
|
|
|
|
+ cpuacct_stats_read(css_ca(css), &val);
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ val[CPUACCT_STAT_USER] *= TICK_NSEC;
|
|
|
|
|
|
|
|
+ val[CPUACCT_STAT_SYSTEM] *= TICK_NSEC;
|
|
|
|
|
|
|
|
+ do_div(usage, NSEC_PER_USEC);
|
|
|
|
|
|
|
|
+ do_div(val[CPUACCT_STAT_USER], NSEC_PER_USEC);
|
|
|
|
|
|
|
|
+ do_div(val[CPUACCT_STAT_SYSTEM], NSEC_PER_USEC);
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ seq_printf(sf, "usage_usec %llu\n"
|
|
|
|
|
|
|
|
+ "user_usec %llu\n"
|
|
|
|
|
|
|
|
+ "system_usec %llu\n",
|
|
|
|
|
|
|
|
+ usage, val[CPUACCT_STAT_USER], val[CPUACCT_STAT_SYSTEM]);
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ css_put(css);
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
|
|
|
* charge this task's execution time to its accounting group.
|
|
|
|
|
|
|
|
*
|
|
|
|
|
|
|
|
diff --git a/kernel/sched/cpuacct.h b/kernel/sched/cpuacct.h
|
|
|
|
|
|
|
|
index ba72807c73d4..ddf7af466d35 100644
|
|
|
|
|
|
|
|
--- a/kernel/sched/cpuacct.h
|
|
|
|
|
|
|
|
+++ b/kernel/sched/cpuacct.h
|
|
|
|
|
|
|
|
@@ -2,6 +2,7 @@
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
extern void cpuacct_charge(struct task_struct *tsk, u64 cputime);
|
|
|
|
|
|
|
|
extern void cpuacct_account_field(struct task_struct *tsk, int index, u64 val);
|
|
|
|
|
|
|
|
+extern void cpuacct_cpu_stats_show(struct seq_file *sf);
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
#else
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
@@ -14,4 +15,8 @@ cpuacct_account_field(struct task_struct *tsk, int index, u64 val)
|
|
|
|
|
|
|
|
{
|
|
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
+static inline void cpuacct_cpu_stats_show(struct seq_file *sf)
|
|
|
|
|
|
|
|
+{
|
|
|
|
|
|
|
|
+}
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
#endif
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
commit 5019fe3d7ec456b58d451ef06fe1f81d7d9f28a9
|
|
|
|
|
|
|
|
Author: Tejun Heo <tj@kernel.org>
|
|
|
|
|
|
|
|
Date: Fri Aug 5 12:41:01 2016 -0400
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
cgroup: add documentation regarding CPU controller cgroup v2 support
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Signed-off-by: Tejun Heo <tj@kernel.org>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
diff --git a/Documentation/cgroup-v2-cpu.txt b/Documentation/cgroup-v2-cpu.txt
|
|
|
|
|
|
|
|
new file mode 100644
|
|
|
|
|
|
|
|
index 000000000000..1ed7032d4472
|
|
|
|
|
|
|
|
--- /dev/null
|
|
|
|
|
|
|
|
+++ b/Documentation/cgroup-v2-cpu.txt
|
|
|
|
|
|
|
|
@@ -0,0 +1,368 @@
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+CPU Controller on Control Group v2
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+August, 2016 Tejun Heo <tj@kernel.org>
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+While most controllers have support for cgroup v2 now, the CPU
|
|
|
|
|
|
|
|
+controller support is not upstream yet due to objections from the
|
|
|
|
|
|
|
|
+scheduler maintainers on the basic designs of cgroup v2. This
|
|
|
|
|
|
|
|
+document explains the current situation as well as an interim
|
|
|
|
|
|
|
|
+solution, and details the disagreements and arguments. The latest
|
|
|
|
|
|
|
|
+version of this document can be found at the following URL.
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git/tree/Documentation/cgroup-v2-cpu.txt?h=cgroup-v2-cpu
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+This document was posted to the linux-kernel and cgroup mailing lists.
|
|
|
|
|
|
|
|
+Unfortunately, no consensus was reached as of Oct, 2016. The thread
|
|
|
|
|
|
|
|
+can be found at the following URL.
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ http://lkml.kernel.org/r/20160805170752.GK2542@mtj.duckdns.org
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+CONTENTS
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+1. Current Situation and Interim Solution
|
|
|
|
|
|
|
|
+2. Disagreements and Arguments
|
|
|
|
|
|
|
|
+ 2-1. Contentious Restrictions
|
|
|
|
|
|
|
|
+ 2-1-1. Process Granularity
|
|
|
|
|
|
|
|
+ 2-1-2. No Internal Process Constraint
|
|
|
|
|
|
|
|
+ 2-2. Impact on CPU Controller
|
|
|
|
|
|
|
|
+ 2-2-1. Impact of Process Granularity
|
|
|
|
|
|
|
|
+ 2-2-2. Impact of No Internal Process Constraint
|
|
|
|
|
|
|
|
+ 2-3. Arguments for cgroup v2
|
|
|
|
|
|
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+3. Way Forward
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+4. References
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+
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+
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+1. Current Situation and Interim Solution
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+
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+All objections from the scheduler maintainers apply to cgroup v2 core
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+design, and there are no known objections to the specifics of the CPU
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+controller cgroup v2 interface. The only blocked part is changes to
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+expose the CPU controller interface on cgroup v2, which comprises the
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+following two patches:
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+
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+ [1] sched: Misc preps for cgroup unified hierarchy interface
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+ [2] sched: Implement interface for cgroup unified hierarchy
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+
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+The necessary changes are superficial and implement the interface
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+files on cgroup v2. The combined diffstat is as follows.
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+
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+ kernel/sched/core.c | 149 +++++++++++++++++++++++++++++++++++++++++++++++--
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+ kernel/sched/cpuacct.c | 57 ++++++++++++------
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+ kernel/sched/cpuacct.h | 5 +
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+ 3 files changed, 189 insertions(+), 22 deletions(-)
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+
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+The patches are easy to apply and forward-port. The following git
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+branch will always carry the two patches on top of the latest release
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+of the upstream kernel.
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+
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+ git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git/cgroup-v2-cpu
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+
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+There also are versioned branches going back to v4.4.
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+
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+ git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git/cgroup-v2-cpu-$KERNEL_VER
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+
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+While it's difficult to tell whether the CPU controller support will
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+be merged, there are crucial resource control features in cgroup v2
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+that are only possible due to the design choices that are being
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+objected to, and every effort will be made to ease enabling the CPU
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+controller cgroup v2 support out-of-tree for parties which choose to.
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+
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+
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+2. Disagreements and Arguments
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+
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+There have been several lengthy discussion threads [3][4] on LKML
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+around the structural constraints of cgroup v2. The two that affect
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+the CPU controller are process granularity and no internal process
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+constraint. Both arise primarily from the need for common resource
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+domain definition across different resources.
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+
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+The common resource domain is a powerful concept in cgroup v2 that
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+allows controllers to make basic assumptions about the structural
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+organization of processes and controllers inside the cgroup hierarchy,
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+and thus solve problems spanning multiple types of resources. The
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+prime example for this is page cache writeback: dirty page cache is
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+regulated through throttling buffered writers based on memory
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+availability, and initiating batched write outs to the disk based on
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+IO capacity. Tracking and controlling writeback inside a cgroup thus
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+requires the direct cooperation of the memory and the IO controller.
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+
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+This easily extends to other areas, such as CPU cycles consumed while
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+performing memory reclaim or IO encryption.
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+
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+
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+2-1. Contentious Restrictions
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+
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+For controllers of different resources to work together, they must
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+agree on a common organization. This uniform model across controllers
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+imposes two contentious restrictions on the CPU controller: process
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+granularity and the no-internal-process constraint.
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+
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+
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+ 2-1-1. Process Granularity
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+
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+ For memory, because an address space is shared between all threads
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+ of a process, the terminal consumer is a process, not a thread.
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+ Separating the threads of a single process into different memory
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+ control domains doesn't make semantical sense. cgroup v2 ensures
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+ that all controller can agree on the same organization by requiring
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+ that threads of the same process belong to the same cgroup.
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+
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+ There are other reasons to enforce process granularity. One
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+ important one is isolating system-level management operations from
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+ in-process application operations. The cgroup interface, being a
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+ virtual filesystem, is very unfit for multiple independent
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+ operations taking place at the same time as most operations have to
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+ be multi-step and there is no way to synchronize multiple accessors.
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+ See also [5] Documentation/cgroup-v2.txt, "R-2. Thread Granularity"
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+
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+
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+ 2-1-2. No Internal Process Constraint
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+
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+ cgroup v2 does not allow processes to belong to any cgroup which has
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+ child cgroups when resource controllers are enabled on it (the
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+ notable exception being the root cgroup itself). This is because,
|
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+ for some resources, a resource domain (cgroup) is not directly
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+ comparable to the terminal consumer (process/task) of said resource,
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+ and so putting the two into a sibling relationship isn't meaningful.
|
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+
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+ - Differing Control Parameters and Capabilities
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+
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+ A cgroup controller has different resource control parameters and
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+ capabilities from a terminal consumer, be that a task or process.
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+ There are a couple cases where a cgroup control knob can be mapped
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+ to a per-task or per-process API but they are exceptions and the
|
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+ mappings aren't obvious even in those cases.
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+
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+ For example, task priorities (also known as nice values) set
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+ through setpriority(2) are mapped to the CPU controller
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+ "cpu.shares" values. However, how exactly the two ranges map and
|
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+ even the fact that they map to each other at all are not obvious.
|
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+
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+ The situation gets further muddled when considering other resource
|
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+ types and control knobs. IO priorities set through ioprio_set(2)
|
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+ cannot be mapped to IO controller weights and most cgroup resource
|
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+ control knobs including the bandwidth control knobs of the CPU
|
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+ controller don't have counterparts in the terminal consumers.
|
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+
|
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+ - Anonymous Resource Consumption
|
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+
|
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+ For CPU, every time slice consumed from inside a cgroup, which
|
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+ comprises most but not all of consumed CPU time for the cgroup,
|
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+ can be clearly attributed to a specific task or process. Because
|
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+ these two types of entities are directly comparable as consumers
|
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+ of CPU time, it's theoretically possible to mix tasks and cgroups
|
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+ on the same tree levels and let them directly compete for the time
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+ quota available to their common ancestor.
|
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+
|
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+ However, the same can't be said for resource types like memory or
|
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+ IO: the memory consumed by the page cache, for example, can be
|
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+ tracked on a per-cgroup level, but due to mismatches in lifetimes
|
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+ of involved objects (page cache can persist long after processes
|
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+ are gone), shared usages and the implementation overhead of
|
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+ tracking persistent state, it can no longer be attributed to
|
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|
+ individual processes after instantiation. Consequently, any IO
|
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+ incurred by page cache writeback can be attributed to a cgroup,
|
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+ but not to the individual consumers inside the cgroup.
|
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+
|
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+ For memory and IO, this makes a resource domain (cgroup) an object
|
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|
+ of a fundamentally different type than a terminal consumer
|
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|
+ (process). A process can't be a first class object in the resource
|
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+ distribution graph as its total resource consumption can't be
|
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+ described without the containing resource domain.
|
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+
|
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+ Disallowing processes in internal cgroups avoids competition between
|
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+ cgroups and processes which cannot be meaningfully defined for these
|
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+ resources. All resource control takes place among cgroups and a
|
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+ terminal consumer interacts with the containing cgroup the same way
|
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+ it would with the system without cgroup.
|
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+
|
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+ Root cgroup is exempt from this constraint, which is in line with
|
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+ how root cgroup is handled in general - it's excluded from cgroup
|
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+ resource accounting and control.
|
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+
|
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+
|
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+Enforcing process granularity and no internal process constraint
|
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|
|
|
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|
+allows all controllers to be on the same footing in terms of resource
|
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+distribution hierarchy.
|
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+
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+
|
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|
+2-2. Impact on CPU Controller
|
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+
|
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|
+As indicated earlier, the CPU controller's resource distribution graph
|
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|
|
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|
+is the simplest. Every schedulable resource consumption can be
|
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|
+attributed to a specific task. In addition, for weight based control,
|
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|
+the per-task priority set through setpriority(2) can be translated to
|
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|
+and from a per-cgroup weight. As such, the CPU controller can treat a
|
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|
+task and a cgroup symmetrically, allowing support for any tree layout
|
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|
+of cgroups and tasks. Both process granularity and the no internal
|
|
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|
|
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+process constraint restrict how the CPU controller can be used.
|
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+
|
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+
|
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+ 2-2-1. Impact of Process Granularity
|
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+
|
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|
|
+ Process granularity prevents tasks belonging to the same process to
|
|
|
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|
+ be assigned to different cgroups. It was pointed out [6] that this
|
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|
+ excludes the valid use case of hierarchical CPU distribution within
|
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+ processes.
|
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+
|
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|
+ To address this issue, the rgroup (resource group) [7][8][9]
|
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|
|
|
|
|
+ interface, an extension of the existing setpriority(2) API, was
|
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|
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|
+ proposed, which is in line with other programmable priority
|
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|
+ mechanisms and eliminates the risk of in-application configuration
|
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|
+ and system configuration stepping on each other's toes.
|
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|
|
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|
|
+ Unfortunately, the proposal quickly turned into discussions around
|
|
|
|
|
|
|
|
+ cgroup v2 design decisions [4] and no consensus could be reached.
|
|
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+
|
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+
|
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|
|
+ 2-2-2. Impact of No Internal Process Constraint
|
|
|
|
|
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|
|
+
|
|
|
|
|
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|
|
+ The no internal process constraint disallows tasks from competing
|
|
|
|
|
|
|
|
+ directly against cgroups. Here is an excerpt from Peter Zijlstra
|
|
|
|
|
|
|
|
+ pointing out the issue [10] - R, L and A are cgroups; t1, t2, t3 and
|
|
|
|
|
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|
|
+ t4 are tasks:
|
|
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|
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+
|
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+
|
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+ R
|
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+ / | \
|
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+ t1 t2 A
|
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+ / \
|
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|
+ t3 t4
|
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+
|
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|
|
|
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+
|
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|
+ Is fundamentally different from:
|
|
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|
|
|
|
+
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+ R
|
|
|
|
|
|
|
|
+ / \
|
|
|
|
|
|
|
|
+ L A
|
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|
+ / \ / \
|
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|
|
|
+ t1 t2 t3 t4
|
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|
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+
|
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+
|
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|
+ Because if in the first hierarchy you add a task (t5) to R, all of
|
|
|
|
|
|
|
|
+ its A will run at 1/4th of total bandwidth where before it had
|
|
|
|
|
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|
|
+ 1/3rd, whereas with the second example, if you add our t5 to L, A
|
|
|
|
|
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|
+ doesn't get any less bandwidth.
|
|
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|
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+
|
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|
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+
|
|
|
|
|
|
|
|
+ It is true that the trees are semantically different from each other
|
|
|
|
|
|
|
|
+ and the symmetric handling of tasks and cgroups is aesthetically
|
|
|
|
|
|
|
|
+ pleasing. However, it isn't clear what the practical usefulness of
|
|
|
|
|
|
|
|
+ a layout with direct competition between tasks and cgroups would be,
|
|
|
|
|
|
|
|
+ considering that number and behavior of tasks are controlled by each
|
|
|
|
|
|
|
|
+ application, and cgroups primarily deal with system level resource
|
|
|
|
|
|
|
|
+ distribution; changes in the number of active threads would directly
|
|
|
|
|
|
|
|
+ impact resource distribution. Real world use cases of such layouts
|
|
|
|
|
|
|
|
+ could not be established during the discussions.
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+
|
|
|
|
|
|
|
|
+2-3. Arguments for cgroup v2
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+
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+There are strong demands for comprehensive hierarchical resource
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+control across all major resources, and establishing a common resource
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+hierarchy is an essential step. As with most engineering decisions,
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+common resource hierarchy definition comes with its trade-offs. With
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+cgroup v2, the trade-offs are in the form of structural constraints
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+which, among others, restrict the CPU controller's space of possible
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+configurations.
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+
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+However, even with the restrictions, cgroup v2, in combination with
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+rgroup, covers most of identified real world use cases while enabling
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+new important use cases of resource control across multiple resource
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+types that were fundamentally broken previously.
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+
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+Furthermore, for resource control, treating resource domains as
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+objects of a different type from terminal consumers has important
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+advantages - it can account for resource consumptions which are not
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+tied to any specific terminal consumer, be that a task or process, and
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+allows decoupling resource distribution controls from in-application
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+APIs. Even the CPU controller may benefit from it as the kernel can
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+consume significant amount of CPU cycles in interrupt context or tasks
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+shared across multiple resource domains (e.g. softirq).
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+
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+Finally, it's important to note that enabling cgroup v2 support for
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+the CPU controller doesn't block use cases which require the features
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+which are not available on cgroup v2. Unlikely, but should anybody
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+actually rely on the CPU controller's symmetric handling of tasks and
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+cgroups, backward compatibility is and will be maintained by being
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+able to disconnect the controller from the cgroup v2 hierarchy and use
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+it standalone. This also holds for cpuset which is often used in
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+highly customized configurations which might be a poor fit for common
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+resource domains.
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+
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+The required changes are minimal, the benefits for the target use
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+cases are critical and obvious, and use cases which have to use v1 can
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+continue to do so.
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+
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+
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+3. Way Forward
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+
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+cgroup v2 primarily aims to solve the problem of comprehensive
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+hierarchical resource control across all major computing resources,
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+which is one of the core problems of modern server infrastructure
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+engineering. The trade-offs that cgroup v2 took are results of
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+pursuing that goal and gaining a better understanding of the nature of
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+resource control in the process.
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+
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+I believe that real world usages will prove cgroup v2's model right,
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+considering the crucial pieces of comprehensive resource control that
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+cannot be implemented without common resource domains. This is not to
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+say that cgroup v2 is fixed in stone and can't be updated; if there is
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+an approach which better serves both comprehensive resource control
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+and the CPU controller's flexibility, we will surely move towards
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+that. It goes without saying that discussions around such approach
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+should consider practical aspects of resource control as a whole
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+rather than absolutely focusing on a particular controller.
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+
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+Until such consensus can be reached, the CPU controller cgroup v2
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+support will be maintained out of the mainline kernel in an easily
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+accessible form. If there is anything cgroup developers can do to
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+ease the pain, please feel free to contact us on the cgroup mailing
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+list at cgroups@vger.kernel.org.
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+
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+
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+4. References
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+
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+[1] http://lkml.kernel.org/r/20160105164834.GE5995@mtj.duckdns.org
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+ [PATCH 1/2] sched: Misc preps for cgroup unified hierarchy interface
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+ Tejun Heo <tj@kernel.org>
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+
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+[2] http://lkml.kernel.org/r/20160105164852.GF5995@mtj.duckdns.org
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+ [PATCH 2/2] sched: Implement interface for cgroup unified hierarchy
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+ Tejun Heo <tj@kernel.org>
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+
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+[3] http://lkml.kernel.org/r/1438641689-14655-4-git-send-email-tj@kernel.org
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+ [PATCH 3/3] sched: Implement interface for cgroup unified hierarchy
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+ Tejun Heo <tj@kernel.org>
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+
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+[4] http://lkml.kernel.org/r/20160407064549.GH3430@twins.programming.kicks-ass.net
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+ Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource group and PRIO_RGRP
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+ Peter Zijlstra <peterz@infradead.org>
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+
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+[5] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/cgroup-v2.txt
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+ Control Group v2
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+ Tejun Heo <tj@kernel.org>
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+
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+[6] http://lkml.kernel.org/r/CAPM31RJNy3jgG=DYe6GO=wyL4BPPxwUm1f2S6YXacQmo7viFZA@mail.gmail.com
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+ Re: [PATCH 3/3] sched: Implement interface for cgroup unified hierarchy
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+ Paul Turner <pjt@google.com>
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+
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+[7] http://lkml.kernel.org/r/20160105154503.GC5995@mtj.duckdns.org
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+ [RFD] cgroup: thread granularity support for cpu controller
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+ Tejun Heo <tj@kernel.org>
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+
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+[8] http://lkml.kernel.org/r/1457710888-31182-1-git-send-email-tj@kernel.org
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+ [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource group and PRIO_RGRP
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+ Tejun Heo <tj@kernel.org>
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+
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+[9] http://lkml.kernel.org/r/20160311160522.GA24046@htj.duckdns.org
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+ Example program for PRIO_RGRP
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+ Tejun Heo <tj@kernel.org>
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+
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+[10] http://lkml.kernel.org/r/20160407082810.GN3430@twins.programming.kicks-ass.net
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+ Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource
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+ Peter Zijlstra <peterz@infradead.org>
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