linux-kernel - [PATCH V3 5/6] perf/core: calculate side-band events overhead

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Date:   Thu,  8 Dec 2016 16:27:13 -0500
From:   kan.liang@...el.com
To:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     alexander.shishkin@...ux.intel.com, tglx@...utronix.de,
        namhyung@...nel.org, jolsa@...nel.org, adrian.hunter@...el.com,
        wangnan0@...wei.com, mark.rutland@....com, andi@...stfloor.org,
        Kan Liang <kan.liang@...el.com>
Subject: [PATCH V3 5/6] perf/core: calculate side-band events overhead

From: Kan Liang <kan.liang@...el.com>

Iterating all events which need to receive side-band events also bring
some overhead.

The side-band events overhead PERF_CORE_SB_OVERHEAD is a common overhead
type.

Signed-off-by: Kan Liang <kan.liang@...el.com>
---
 include/uapi/linux/perf_event.h |  1 +
 kernel/events/core.c            | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index c488336..7ba6d30 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1002,6 +1002,7 @@ struct perf_branch_entry {
 enum perf_record_overhead_type {
 	/* common overhead */
 	PERF_CORE_MUX_OVERHEAD	= 0,
+	PERF_CORE_SB_OVERHEAD,
 	/* PMU specific */
 	PERF_OVERHEAD_MAX,
 };
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 28468ae..335b1e2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6134,9 +6134,13 @@ 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_cpu_context *cpuctx;
 	struct perf_event_context *ctx;
+	u64 start_clock, end_clock;
 	int ctxn;
 
+	start_clock = perf_clock();
 	rcu_read_lock();
 	preempt_disable();
 
@@ -6154,12 +6158,23 @@ 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();
+
+	/* calculate side-band event overhead */
+	end_clock = perf_clock();
+	if (overhead_ctx && overhead_ctx->pmu && overhead_ctx->pmu->stat) {
+		cpuctx = this_cpu_ptr(overhead_ctx->pmu->pmu_cpu_context);
+		cpuctx->overhead[PERF_CORE_SB_OVERHEAD].nr++;
+		cpuctx->overhead[PERF_CORE_SB_OVERHEAD].time += end_clock - start_clock;
+	}
 }
 
 /*
-- 
2.4.3