Commit fd7d5517 authored by Ian Rogers's avatar Ian Rogers Committed by Ingo Molnar
Browse files

perf/cgroups: Don't rotate events for cgroups unnecessarily 



Currently perf_rotate_context assumes that if the context's nr_events !=
nr_active a rotation is necessary for perf event multiplexing. With
cgroups, nr_events is the total count of events for all cgroups and
nr_active will not include events in a cgroup other than the current
task's. This makes rotation appear necessary for cgroups when it is not.

Add a perf_event_context flag that is set when rotation is necessary.
Clear the flag during sched_out and set it when a flexible sched_in
fails due to resources.

Signed-off-by: default avatarIan Rogers <irogers@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: https://lkml.kernel.org/r/20190601082722.44543-1-irogers@google.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 637d97b5

include/linux/perf_event.h

+5 −0
Original line number Diff line number Diff line
@@ -749,6 +749,11 @@ struct perf_event_context { 
	int				nr_stat;

	int				nr_freq;

	int				rotate_disable;

	/*

	 * Set when nr_events != nr_active, except tolerant to events not

	 * necessary to be active due to scheduling constraints, such as cgroups.

	 */

	int				rotate_necessary;

	refcount_t			refcount;

	struct task_struct		*task;

kernel/events/core.c

+22 −20
Original line number Diff line number Diff line
@@ -2952,6 +2952,12 @@ static void ctx_sched_out(struct perf_event_context *ctx, 
	if (!ctx->nr_active || !(is_active & EVENT_ALL))

		return;



	/*

	 * If we had been multiplexing, no rotations are necessary, now no events

	 * are active.

	 */

	ctx->rotate_necessary = 0;



	perf_pmu_disable(ctx->pmu);

	if (is_active & EVENT_PINNED) {

		list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list)
@@ -3319,10 +3325,13 @@ static int flexible_sched_in(struct perf_event *event, void *data) 
		return 0;



	if (group_can_go_on(event, sid->cpuctx, sid->can_add_hw)) {

		if (!group_sched_in(event, sid->cpuctx, sid->ctx))

			list_add_tail(&event->active_list, &sid->ctx->flexible_active);

		else

		int ret = group_sched_in(event, sid->cpuctx, sid->ctx);

		if (ret) {

			sid->can_add_hw = 0;

			sid->ctx->rotate_necessary = 1;

			return 0;

		}

		list_add_tail(&event->active_list, &sid->ctx->flexible_active);

	}



	return 0;
@@ -3690,24 +3699,17 @@ ctx_first_active(struct perf_event_context *ctx) 
static bool perf_rotate_context(struct perf_cpu_context *cpuctx)

{

	struct perf_event *cpu_event = NULL, *task_event = NULL;

	bool cpu_rotate = false, task_rotate = false;

	struct perf_event_context *ctx = NULL;

	struct perf_event_context *task_ctx = NULL;

	int cpu_rotate, task_rotate;



	/*

	 * Since we run this from IRQ context, nobody can install new

	 * events, thus the event count values are stable.

	 */



	if (cpuctx->ctx.nr_events) {

		if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)

			cpu_rotate = true;

	}



	ctx = cpuctx->task_ctx;

	if (ctx && ctx->nr_events) {

		if (ctx->nr_events != ctx->nr_active)

			task_rotate = true;

	}

	cpu_rotate = cpuctx->ctx.rotate_necessary;

	task_ctx = cpuctx->task_ctx;

	task_rotate = task_ctx ? task_ctx->rotate_necessary : 0;



	if (!(cpu_rotate || task_rotate))

		return false;
@@ -3716,7 +3718,7 @@ static bool perf_rotate_context(struct perf_cpu_context *cpuctx) 
	perf_pmu_disable(cpuctx->ctx.pmu);



	if (task_rotate)

		task_event = ctx_first_active(ctx);

		task_event = ctx_first_active(task_ctx);

	if (cpu_rotate)

		cpu_event = ctx_first_active(&cpuctx->ctx);
@@ -3724,17 +3726,17 @@ static bool perf_rotate_context(struct perf_cpu_context *cpuctx) 
	 * As per the order given at ctx_resched() first 'pop' task flexible

	 * and then, if needed CPU flexible.

	 */

	if (task_event || (ctx && cpu_event))

		ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE);

	if (task_event || (task_ctx && cpu_event))

		ctx_sched_out(task_ctx, cpuctx, EVENT_FLEXIBLE);

	if (cpu_event)

		cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);



	if (task_event)

		rotate_ctx(ctx, task_event);

		rotate_ctx(task_ctx, task_event);

	if (cpu_event)

		rotate_ctx(&cpuctx->ctx, cpu_event);



	perf_event_sched_in(cpuctx, ctx, current);

	perf_event_sched_in(cpuctx, task_ctx, current);



	perf_pmu_enable(cpuctx->ctx.pmu);

	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);

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