perf: Provide better condition for event rotation

Try to avoid useless rotation and PMU disables.

[ Could be improved by keeping a nr_runnable count to better account
  for the < PERF_STAT_INACTIVE counters ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: paulus@samba.org
Cc: eranian@google.com
Cc: robert.richter@amd.com
Cc: fweisbec@gmail.com
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 6 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index d8108465397d..52c69a34d697 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1524,12 +1524,15 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx)
                  */
                 if (interrupts == MAX_INTERRUPTS) {
                         perf_log_throttle(event, 1);
+                        perf_disable();
                         event->pmu->unthrottle(event);
+                        perf_enable();
                 }
 
                 if (!event->attr.freq || !event->attr.sample_freq)
                         continue;
 
+                perf_disable();
                 event->pmu->read(event);
                 now = atomic64_read(&event->count);
                 delta = now - hwc->freq_count_stamp;
@@ -1537,6 +1540,7 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx)
 
                 if (delta > 0)
                         perf_adjust_period(event, TICK_NSEC, delta);
+                perf_enable();
         }
         raw_spin_unlock(&ctx->lock);
 }
@@ -1546,9 +1550,6 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx)
  */
 static void rotate_ctx(struct perf_event_context *ctx)
 {
-        if (!ctx->nr_events)
-                return;
-
         raw_spin_lock(&ctx->lock);
 
         /* Rotate the first entry last of non-pinned groups */
@@ -1561,19 +1562,28 @@ void perf_event_task_tick(struct task_struct *curr)
 {
         struct perf_cpu_context *cpuctx;
         struct perf_event_context *ctx;
+        int rotate = 0;
 
         if (!atomic_read(&nr_events))
                 return;
 
         cpuctx = &__get_cpu_var(perf_cpu_context);
-        ctx = curr->perf_event_ctxp;
+        if (cpuctx->ctx.nr_events &&
+            cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
+                rotate = 1;
 
-        perf_disable();
+        ctx = curr->perf_event_ctxp;
+        if (ctx && ctx->nr_events && ctx->nr_events != ctx->nr_active)
+                rotate = 1;
 
         perf_ctx_adjust_freq(&cpuctx->ctx);
         if (ctx)
                 perf_ctx_adjust_freq(ctx);
 
+        if (!rotate)
+                return;
+
+        perf_disable();
         cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
         if (ctx)
                 task_ctx_sched_out(ctx, EVENT_FLEXIBLE);
@@ -1585,7 +1595,6 @@ void perf_event_task_tick(struct task_struct *curr)
         cpu_ctx_sched_in(cpuctx, EVENT_FLEXIBLE);
         if (ctx)
                 task_ctx_sched_in(curr, EVENT_FLEXIBLE);
-
         perf_enable();
 }