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

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Message-ID: <20251118110309.GP3245006@noisy.programming.kicks-ass.net>
Date: Tue, 18 Nov 2025 12:03:09 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: 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>, 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>
Subject: Re: [PATCH] perf: Fix 0 count issue of cpu-clock

On Wed, Nov 12, 2025 at 04:05:26PM +0800, Dapeng Mi wrote:

> 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);
>  }

I think it can both just be: PERF_EF_UPDATE. The only pmu::del() caller
hands in flags=0, but if there were to be flags added, we'd have to
audit all del methods anyway.

Also, the few comments we do have already note that ->del() must do
->stop(EF_UPDATE).