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authorIan Rogers <irogers@google.com>2019-06-01 01:27:22 -0700
committerIngo Molnar <mingo@kernel.org>2019-06-24 19:30:04 +0200
commitfd7d55172d1e2e501e6da0a5c1de25f06612dc2e (patch)
tree4521b1d53d01c694a8f7b20254ff893b49b8a151
parent637d97b53cdded02da55d0a25cda6fd6af3bd042 (diff)
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: Ian Rogers <irogers@google.com> Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
-rw-r--r--include/linux/perf_event.h5
-rw-r--r--kernel/events/core.c42
2 files changed, 27 insertions, 20 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3dc01cf98e16..2ddae518dce6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -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;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 118ad1aef6af..23efe6792abc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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);