Messages in this thread | | | Date | Tue, 30 Apr 2019 10:56:40 +0200 | From | Peter Zijlstra <> | 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:
> 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;
If you're not adding more bits, why not just keep it an int?
> #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); > }
That is a bit of a hack...
> @@ -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 > group_sched_out(event, cpuctx, ctx); > + } > }
This works by accident, however..
> > 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); > }
this one is just wrong afaict.
Suppose the new cgroup has pinned events, which we cannot schedule because you left !cgroup flexible events on.
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