linux-kernel - [PATCH V2 03/13] perf/x86: output sampling overhead

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Date:   Fri,  2 Dec 2016 16:19:11 -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 V2 03/13] perf/x86: output 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          | 17 ++++++++++++++++-
 arch/x86/events/perf_event.h    |  2 ++
 include/uapi/linux/perf_event.h |  1 +
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 9d4bf3a..de40f96 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1397,6 +1397,9 @@ static void x86_pmu_del(struct perf_event *event, int flags)
 
 	perf_event_update_userpage(event);
 
+	if ((flags & PERF_EF_LOG) && cpuc->nmi_overhead.nr)
+		perf_log_overhead(event, PERF_PMU_SAMPLE_OVERHEAD, &cpuc->nmi_overhead);
+
 do_del:
 	if (x86_pmu.del) {
 		/*
@@ -1475,11 +1478,21 @@ void perf_events_lapic_init(void)
 	apic_write(APIC_LVTPC, APIC_DM_NMI);
 }
 
+static void
+perf_calculate_nmi_overhead(u64 time)
+{
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	cpuc->nmi_overhead.nr++;
+	cpuc->nmi_overhead.time += time;
+}
+
 static int
 perf_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
 {
 	u64 start_clock;
 	u64 finish_clock;
+	u64 clock;
 	int ret;
 
 	/*
@@ -1492,8 +1505,10 @@ 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(finish_clock - start_clock);
+	perf_calculate_nmi_overhead(clock);
+	perf_sample_event_took(clock);
 
 	return ret;
 }
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index a77ee02..7a03384 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -230,6 +230,8 @@ struct cpu_hw_events {
 	struct intel_excl_cntrs		*excl_cntrs;
 	int excl_thread_id; /* 0 or 1 */
 
+	struct perf_overhead_entry     nmi_overhead;
+
 	/*
 	 * AMD specific bits
 	 */
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index bb0ecf0..fe7b1fb 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1001,6 +1001,7 @@ enum perf_record_overhead_type {
 	PERF_CORE_OVERHEAD	 = 0,
 
 	PERF_PMU_OVERHEAD	 = 20,
+	PERF_PMU_SAMPLE_OVERHEAD = 20,
 
 	PERF_OVERHEAD_MAX,
 };
-- 
2.5.5