Messages in this thread | | | Subject | Re: [PATCH 1/4] perf: Fix system-wide events miscounting during cgroup monitoring | From | "Liang, Kan" <> | Date | Mon, 29 Apr 2019 11:27:47 -0400 |
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On 4/29/2019 11:04 AM, Mark Rutland wrote: > On Mon, Apr 29, 2019 at 07:44:02AM -0700, kan.liang@linux.intel.com wrote: >> From: Kan Liang <kan.liang@linux.intel.com> >> >> When counting system-wide events and cgroup events simultaneously, the >> value of system-wide events are miscounting. For example, >> >> perf stat -e cycles,instructions -e cycles,instructions -G >> cgroup1,cgroup1,cgroup2,cgroup2 -a -e cycles,instructions -I 1000 >> >> 1.096265502 12,375,398,872 cycles cgroup1 >> 1.096265502 8,396,184,503 instructions cgroup1 >> # 0.10 insn per cycle >> 1.096265502 109,609,027,112 cycles cgroup2 >> 1.096265502 11,533,690,148 instructions cgroup2 >> # 0.14 insn per cycle >> 1.096265502 121,672,937,058 cycles >> 1.096265502 19,331,496,727 instructions # >> 0.24 insn per cycle >> >> The events are identical events for system-wide and cgroup. The >> value of system-wide events is less than the sum of cgroup events, >> which is wrong. >> >> Both system-wide and cgroup are per-cpu. They share the same cpuctx >> groups, cpuctx->flexible_groups/pinned_groups. >> In context switch, cgroup switch tries to schedule all the events in >> the cpuctx groups. The unmatched cgroup events can be filtered by its >> event->cgrp. However, system-wide events, which event->cgrp is NULL, are >> unconditionally switched, which causes miscounting. > > Why exactly does that cause mis-counting? > > Are the system-wide events not switched back in? Or filtered > erroneously?
The small period between the prev cgroup sched_out and the new cgroup sched_in is missed for system-wide events. Current code mistakenly sched_out of system-wide events during that period.
> >> Introduce cgrp_switch in cpuctx to indicate the cgroup context switch. >> If it's system-wide event in context switch, don't try to switch it. >> >> Fixes: e5d1367f17ba ("perf: Add cgroup support") >> Signed-off-by: Kan Liang <kan.liang@linux.intel.com> >> --- >> include/linux/perf_event.h | 1 + >> kernel/events/core.c | 30 ++++++++++++++++++++++++++++-- >> 2 files changed, 29 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h >> index e47ef76..039e2f2 100644 >> --- a/include/linux/perf_event.h >> +++ b/include/linux/perf_event.h >> @@ -795,6 +795,7 @@ struct perf_cpu_context { >> #ifdef CONFIG_CGROUP_PERF >> struct perf_cgroup *cgrp; >> struct list_head cgrp_cpuctx_entry; >> + unsigned int cgrp_switch :1; >> #endif >> >> struct list_head sched_cb_entry; >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index dc7dead..388dd42 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -809,6 +809,7 @@ static void perf_cgroup_switch(struct task_struct *task, int mode) >> >> perf_ctx_lock(cpuctx, cpuctx->task_ctx); >> perf_pmu_disable(cpuctx->ctx.pmu); >> + cpuctx->cgrp_switch = true; >> >> if (mode & PERF_CGROUP_SWOUT) { >> cpu_ctx_sched_out(cpuctx, EVENT_ALL); >> @@ -832,6 +833,7 @@ static void perf_cgroup_switch(struct task_struct *task, int mode) >> &cpuctx->ctx); >> cpu_ctx_sched_in(cpuctx, EVENT_ALL, task); >> } >> + cpuctx->cgrp_switch = false; >> perf_pmu_enable(cpuctx->ctx.pmu); >> perf_ctx_unlock(cpuctx, cpuctx->task_ctx); >> } >> @@ -2944,13 +2946,25 @@ static void ctx_sched_out(struct perf_event_context *ctx, >> >> perf_pmu_disable(ctx->pmu); >> if (is_active & EVENT_PINNED) { >> - list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list) >> + list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list) { >> +#ifdef CONFIG_CGROUP_PERF >> + /* Don't sched system-wide event when cgroup context switch */ >> + if (cpuctx->cgrp_switch && !event->cgrp) >> + continue; >> +#endif > > This pattern is duplicated several times, and should probably be a > helper like: > > static bool skip_cgroup_switch(struct perf_cpu_context *cpuctx, > struct perf_event *event); > { > return IS_ENABLED(CONFIG_CGROUP_PERF) && > cpuctx->cgrp_switch && > !event->cgrp; > } > > ... allowing the above to be an unconditional: > > if (skip_cgroup_switch(cpuctx, event)) > continue; > > ... and likewise for the other cases. >
I will change it in V2.
Thanks, Kan
> Thanks, > Mark. > >> group_sched_out(event, cpuctx, ctx); >> + } >> } >> >> if (is_active & EVENT_FLEXIBLE) { >> - list_for_each_entry_safe(event, tmp, &ctx->flexible_active, active_list) >> + list_for_each_entry_safe(event, tmp, &ctx->flexible_active, active_list) { >> +#ifdef CONFIG_CGROUP_PERF >> + /* Don't sched system-wide event when cgroup context switch */ >> + if (cpuctx->cgrp_switch && !event->cgrp) >> + continue; >> +#endif >> group_sched_out(event, cpuctx, ctx); >> + } >> } >> perf_pmu_enable(ctx->pmu); >> } >> @@ -3280,6 +3294,12 @@ static int pinned_sched_in(struct perf_event *event, void *data) >> if (event->state <= PERF_EVENT_STATE_OFF) >> return 0; >> >> +#ifdef CONFIG_CGROUP_PERF >> + /* Don't sched system-wide event when cgroup context switch */ >> + if (sid->cpuctx->cgrp_switch && !event->cgrp) >> + return 0; >> +#endif >> + >> if (!event_filter_match(event)) >> return 0; >> >> @@ -3305,6 +3325,12 @@ static int flexible_sched_in(struct perf_event *event, void *data) >> if (event->state <= PERF_EVENT_STATE_OFF) >> return 0; >> >> +#ifdef CONFIG_CGROUP_PERF >> + /* Don't sched system-wide event when cgroup context switch */ >> + if (sid->cpuctx->cgrp_switch && !event->cgrp) >> + return 0; >> +#endif >> + >> if (!event_filter_match(event)) >> return 0; >> >> -- >> 2.7.4 >>
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