Messages in this thread Patch in this message | | | Date | Mon, 29 Apr 2019 16:04:43 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 1/4] perf: Fix system-wide events miscounting during cgroup monitoring |
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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?
> 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.
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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