linux-kernel - [PATCH] perf: Fix 0 count issue of cpu-clock

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Message-Id: <20251112080526.3971392-1-dapeng1.mi@linux.intel.com>
Date: Wed, 12 Nov 2025 16:05:26 +0800
From: Dapeng Mi <dapeng1.mi@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Eranian Stephane <eranian@...gle.com>
Cc: linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	Dapeng Mi <dapeng1.mi@...el.com>,
	Zide Chen <zide.chen@...el.com>,
	Falcon Thomas <thomas.falcon@...el.com>,
	Xudong Hao <xudong.hao@...el.com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [PATCH] perf: Fix 0 count issue of cpu-clock

Currently cpu-clock event always returns 0 count, e.g.,

perf stat -e cpu-clock -- sleep 1

 Performance counter stats for 'sleep 1':
                 0      cpu-clock                        #    0.000 CPUs utilized
       1.002308394 seconds time elapsed

The root cause is the commit 'bc4394e5e79c ("perf: Fix the throttle
 error of some clock events")' adds PERF_EF_UPDATE flag check before
calling cpu_clock_event_update() to update the count, however the
PERF_EF_UPDATE flag is never set when the cpu-clock event is stopped in
counting mode (pmu->dev() -> cpu_clock_event_del() ->
cpu_clock_event_stop()). This leads to the cpu-clock event count is
never updated.

To fix this issue, force to set PERF_EF_UPDATE flag for cpu-clock event
just like what task-clock does. Besides, or flags with PERF_EF_UPDATE
for task-clock although currently the flags argument would always be 0.

Fixes: bc4394e5e79c ("perf: Fix the throttle error of some clock events")
Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
---

With this change, both cpu-clock and task-clock can do counting and
samping correctly.

1. perf stat -e cpu-clock,task-clock -- true

 Performance counter stats for 'true':
           240,636      cpu-clock                        #    0.358 CPUs utilized
           243,319      task-clock                       #    0.362 CPUs utilized

2. perf record -e cpu-clock -c 10000 -Iax,bx -- sleep 1
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.028 MB perf.data (36 samples) ]

3. perf record -e task-clock -c 10000 -Iax,bx -- sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.029 MB perf.data (41 samples) ]

 kernel/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f6a08c73f783..77d3af5959c1 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11964,7 +11964,7 @@ static int cpu_clock_event_add(struct perf_event *event, int flags)
 
 static void cpu_clock_event_del(struct perf_event *event, int flags)
 {
-	cpu_clock_event_stop(event, flags);
+	cpu_clock_event_stop(event, flags | PERF_EF_UPDATE);
 }
 
 static void cpu_clock_event_read(struct perf_event *event)
@@ -12043,7 +12043,7 @@ static int task_clock_event_add(struct perf_event *event, int flags)
 
 static void task_clock_event_del(struct perf_event *event, int flags)
 {
-	task_clock_event_stop(event, PERF_EF_UPDATE);
+	task_clock_event_stop(event, flags | PERF_EF_UPDATE);
 }
 
 static void task_clock_event_read(struct perf_event *event)

base-commit: 2093d8cf80fa5552d1025a78a8f3a10bf3b6466e
prerequisite-patch-id: a15bcd62a8dcd219d17489eef88b66ea5488a2a0
prerequisite-patch-id: 2a0eefce67b21d1f30c272fd8115b0dc1aca3897
-- 
2.34.1