linux-kernel - Re: [PATCH] selftests/tracing: Run sample events to clear page cache events

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Message-Id: <20251111082251.2496db7c20b28184cd8cb759@kernel.org>
Date: Tue, 11 Nov 2025 08:22:51 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, linux-kselftest@...r.kernel.org,
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] selftests/tracing: Run sample events to clear page
 cache events

On Tue, 28 Oct 2025 12:27:24 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> The tracing selftest "event-filter-function.tc" was failing because it
> first runs the "sample_events" function that triggers the kmem_cache_free
> event and it looks at what function was used during a call to "ls".
> 
> But the first time it calls this, it could trigger events that are used to
> pull pages into the page cache.
> 
> The rest of the test uses the function it finds during that call to see if
> it will be called in subsequent "sample_events" calls. But if there's no
> need to pull pages into the page cache, it will not trigger that function
> and the test will fail.
> 
> Call the "sample_events" twice to trigger all the page cache work before
> it calls it to find a function to use in subsequent checks.
> 

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thanks,

> Cc: stable@...r.kernel.org
> Fixes: eb50d0f250e96 ("selftests/ftrace: Choose target function for filter test from samples")
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  .../selftests/ftrace/test.d/filter/event-filter-function.tc   | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc b/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc
> index c62165fabd0c..003f612f57b0 100644
> --- a/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc
> +++ b/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc
> @@ -20,6 +20,10 @@ sample_events() {
>  echo 0 > tracing_on
>  echo 0 > events/enable
>  
> +# Clear functions caused by page cache; run sample_events twice
> +sample_events
> +sample_events
> +
>  echo "Get the most frequently calling function"
>  echo > trace
>  sample_events
> -- 
> 2.51.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>