From fd7d55172d1e2e501e6da0a5c1de25f06612dc2e Mon Sep 17 00:00:00 2001 From: Ian Rogers Date: Sat, 1 Jun 2019 01:27:22 -0700 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Arnaldo Carvalho de Melo Cc: Borislav Petkov Cc: Jiri Olsa Cc: Kan Liang Cc: Linus Torvalds Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Link: https://lkml.kernel.org/r/20190601082722.44543-1-irogers@google.com Signed-off-by: Ingo Molnar --- include/linux/perf_event.h | 5 +++++ kernel/events/core.c | 42 ++++++++++++++++++++------------------ 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); -- 2.45.2