linux-kernel - [PATCH V3 4/6] perf/core: calculate multiplexing overhead

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Date:   Thu,  8 Dec 2016 16:27:12 -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 4/6] perf/core: calculate multiplexing overhead

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

Multiplexing overhead is one of the key overhead when the number of
events is more than available counters.

The multiplexing overhead PERF_CORE_MUX_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            | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 23b7963..c488336 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1001,6 +1001,7 @@ struct perf_branch_entry {
  */
 enum perf_record_overhead_type {
 	/* common overhead */
+	PERF_CORE_MUX_OVERHEAD	= 0,
 	/* PMU specific */
 	PERF_OVERHEAD_MAX,
 };
diff --git a/kernel/events/core.c b/kernel/events/core.c
index dbde193..28468ae 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3326,6 +3326,7 @@ static void rotate_ctx(struct perf_event_context *ctx)
 static int perf_rotate_context(struct perf_cpu_context *cpuctx)
 {
 	struct perf_event_context *ctx = NULL;
+	u64 start_clock, end_clock;
 	int rotate = 0;
 
 	if (cpuctx->ctx.nr_events) {
@@ -3342,6 +3343,7 @@ static int perf_rotate_context(struct perf_cpu_context *cpuctx)
 	if (!rotate)
 		goto done;
 
+	start_clock = perf_clock();
 	perf_ctx_lock(cpuctx, cpuctx->task_ctx);
 	perf_pmu_disable(cpuctx->ctx.pmu);
 
@@ -3357,6 +3359,13 @@ static int perf_rotate_context(struct perf_cpu_context *cpuctx)
 
 	perf_pmu_enable(cpuctx->ctx.pmu);
 	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
+
+	/* calculate multiplexing overhead */
+	if (cpuctx->ctx.pmu->stat) {
+		end_clock = perf_clock();
+		cpuctx->overhead[PERF_CORE_MUX_OVERHEAD].nr++;
+		cpuctx->overhead[PERF_CORE_MUX_OVERHEAD].time += end_clock - start_clock;
+	}
 done:
 
 	return rotate;
-- 
2.4.3