[PATCH 04/14] perf/x86: output side-band events overhead

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxx>

Iterating all events which need to receive side-band events also bring
some overhead.
Save the overhead information in task context or CPU context, whichever
context is available.

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
---
 include/linux/perf_event.h      |  2 ++
 include/uapi/linux/perf_event.h |  1 +
 kernel/events/core.c            | 32 ++++++++++++++++++++++++++++----
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f72b97a..ec3cb7f 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -764,6 +764,8 @@ struct perf_event_context {
 #endif
 	void				*task_ctx_data; /* pmu specific data */
 	struct rcu_head			rcu_head;
+
+	struct perf_overhead_entry	sb_overhead;
 };
 
 /*
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 9124c7c..5e7c522 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -994,6 +994,7 @@ struct perf_branch_entry {
 enum perf_record_overhead_type {
 	PERF_NMI_OVERHEAD	= 0,
 	PERF_MUX_OVERHEAD,
+	PERF_SB_OVERHEAD,
 
 	PERF_OVERHEAD_MAX,
 };
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9934059..51e9df7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1829,9 +1829,15 @@ event_sched_out(struct perf_event *event,
 	if (event->attr.exclusive || !cpuctx->active_oncpu)
 		cpuctx->exclusive = 0;
 
-	if (log_overhead && cpuctx->mux_overhead.nr) {
-		cpuctx->mux_overhead.cpu = smp_processor_id();
-		perf_log_overhead(event, PERF_MUX_OVERHEAD, &cpuctx->mux_overhead);
+	if (log_overhead) {
+		if (cpuctx->mux_overhead.nr) {
+			cpuctx->mux_overhead.cpu = smp_processor_id();
+			perf_log_overhead(event, PERF_MUX_OVERHEAD, &cpuctx->mux_overhead);
+		}
+		if (ctx->sb_overhead.nr) {
+			ctx->sb_overhead.cpu = smp_processor_id();
+			perf_log_overhead(event, PERF_SB_OVERHEAD, &ctx->sb_overhead);
+		}
 	}
 
 	perf_pmu_enable(event->pmu);
@@ -6133,6 +6139,14 @@ static void perf_iterate_sb_cpu(perf_iterate_f output, void *data)
 	}
 }
 
+static void
+perf_caculate_sb_overhead(struct perf_event_context *ctx,
+			  u64 time)
+{
+	ctx->sb_overhead.nr++;
+	ctx->sb_overhead.time += time;
+}
+
 /*
  * Iterate all events that need to receive side-band events.
  *
@@ -6143,9 +6157,12 @@ static void
 perf_iterate_sb(perf_iterate_f output, void *data,
 	       struct perf_event_context *task_ctx)
 {
+	struct perf_event_context *overhead_ctx = task_ctx;
 	struct perf_event_context *ctx;
+	u64 start_clock, end_clock;
 	int ctxn;
 
+	start_clock = perf_clock();
 	rcu_read_lock();
 	preempt_disable();
 
@@ -6163,12 +6180,19 @@ perf_iterate_sb(perf_iterate_f output, void *data,
 
 	for_each_task_context_nr(ctxn) {
 		ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
-		if (ctx)
+		if (ctx) {
 			perf_iterate_ctx(ctx, output, data, false);
+			if (!overhead_ctx)
+				overhead_ctx = ctx;
+		}
 	}
 done:
 	preempt_enable();
 	rcu_read_unlock();
+
+	end_clock = perf_clock();
+	if (overhead_ctx)
+		perf_caculate_sb_overhead(overhead_ctx, end_clock - start_clock);
 }
 
 /*
-- 
2.5.5