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>

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3dc01cf98e1647cf3dcf8b93a9a9474a4e3ca631..2ddae518dce64a54b73c175ee40721d04f5032ad 100644 (file)
--- 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 118ad1aef6af0469c784cc7a8521bb6719345fc9..23efe6792abcc3d4bf7ab2c0d2cb028ef618d5d4 100644 (file)
--- 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);