linux-kernel - [PATCH V3 6/6] perf/x86: calculate sampling overhead

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Date:   Thu,  8 Dec 2016 16:27:14 -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 6/6] perf/x86: calculate sampling overhead

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

On x86, NMI handler is the most important part which brings overhead
for sampling. Adding a pmu specific overhead type
PERF_PMU_SAMPLE_OVERHEAD for it.

For other architectures which may don't have NMI, the overhead type can
be reused.

Signed-off-by: Kan Liang <kan.liang@...el.com>
---
 arch/x86/events/core.c          | 8 +++++++-
 include/uapi/linux/perf_event.h | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 09ab36a..1e57ccf 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1478,8 +1478,10 @@ void perf_events_lapic_init(void)
 static int
 perf_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
 {
+	struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu.pmu_cpu_context);
 	u64 start_clock;
 	u64 finish_clock;
+	u64 clock;
 	int ret;
 
 	/*
@@ -1492,8 +1494,12 @@ perf_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
 	start_clock = sched_clock();
 	ret = x86_pmu.handle_irq(regs);
 	finish_clock = sched_clock();
+	clock = finish_clock - start_clock;
+	perf_sample_event_took(clock);
 
-	perf_sample_event_took(finish_clock - start_clock);
+	/* calculate NMI overhead */
+	cpuctx->overhead[PERF_PMU_SAMPLE_OVERHEAD].nr++;
+	cpuctx->overhead[PERF_PMU_SAMPLE_OVERHEAD].time += clock;
 
 	return ret;
 }
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 7ba6d30..954b116 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1004,6 +1004,7 @@ enum perf_record_overhead_type {
 	PERF_CORE_MUX_OVERHEAD	= 0,
 	PERF_CORE_SB_OVERHEAD,
 	/* PMU specific */
+	PERF_PMU_SAMPLE_OVERHEAD,
 	PERF_OVERHEAD_MAX,
 };
 
-- 
2.4.3