linux-kernel - [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live cputime event

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Date:   Thu,  7 Jun 2018 00:15:12 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Milian Wolff <milian.wolff@...b.com>,
        Andi Kleen <andi@...stfloor.org>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live cputime event

Disable stopping of the idle tick when having live cputime
event. When the tick is disabled, the idle counts are out
of date until next tick/update and perf cputime PMU provides
misleading counts.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 include/linux/perf_event.h |  1 +
 kernel/events/cputime.c    | 13 +++++++++++++
 kernel/time/tick-sched.c   |  4 ++++
 3 files changed, 18 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index aa9eaab370be..ba61d2f9602a 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1407,4 +1407,5 @@ int perf_event_exit_cpu(unsigned int cpu);
 #define perf_event_exit_cpu	NULL
 #endif
 
+bool has_cputime_event(int cpu);
 #endif /* _LINUX_PERF_EVENT_H */
diff --git a/kernel/events/cputime.c b/kernel/events/cputime.c
index efad24543f13..32d3cde0047e 100644
--- a/kernel/events/cputime.c
+++ b/kernel/events/cputime.c
@@ -1,6 +1,7 @@
 #include <linux/kernel_stat.h>
 #include <linux/sched.h>
 #include <linux/perf_event.h>
+#include <linux/tick.h>
 
 enum perf_cputime_id {
 	PERF_CPUTIME_USER,
@@ -16,6 +17,13 @@ enum perf_cputime_id {
 	PERF_CPUTIME_MAX,
 };
 
+static DEFINE_PER_CPU(int, has_cputime);
+
+bool has_cputime_event(int cpu)
+{
+	return per_cpu(has_cputime, cpu) != 0;
+}
+
 static enum cpu_usage_stat map[PERF_CPUTIME_MAX] = {
 	[PERF_CPUTIME_USER]		= CPUTIME_USER,
 	[PERF_CPUTIME_NICE]		= CPUTIME_NICE,
@@ -143,12 +151,17 @@ static int cputime_event_add(struct perf_event *event, int flags)
 	if (flags & PERF_EF_START)
 		cputime_event_start(event, flags);
 
+	if (event->hw.config == PERF_CPUTIME_IDLE)
+		tick_nohz_idle_restart_tick();
+
+	this_cpu_inc(has_cputime);
 	return 0;
 }
 
 static void cputime_event_del(struct perf_event *event, int flags)
 {
 	cputime_event_stop(event, PERF_EF_UPDATE);
+	this_cpu_dec(has_cputime);
 }
 
 static void perf_cputime_read(struct perf_event *event)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index da9455a6b42b..1c105bc2a92e 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -28,6 +28,7 @@
 #include <linux/posix-timers.h>
 #include <linux/context_tracking.h>
 #include <linux/mm.h>
+#include <linux/perf_event.h>
 
 #include <asm/irq_regs.h>
 
@@ -912,6 +913,9 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 			return false;
 	}
 
+	if (has_cputime_event(cpu))
+		return false;
+
 	return true;
 }
 
-- 
2.13.6