linux-kernel - Re: [PATCH] perf tools: Skip BPF sideband event for userspace profiling

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Message-ID: <CAPhsuW46wuwoXSf-Vq5Y78b3GeGspA3PqtNMm8GTHXAMmnRNbA@mail.gmail.com>
Date: Wed, 26 Feb 2025 14:00:36 -0800
From: Song Liu <song@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Namhyung Kim <namhyung@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, 
	Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-perf-users@...r.kernel.org, James Clark <james.clark@...aro.org>
Subject: Re: [PATCH] perf tools: Skip BPF sideband event for userspace profiling

On Wed, Feb 26, 2025 at 12:59 PM Ian Rogers <irogers@...gle.com> wrote:
>
> On Wed, Feb 26, 2025 at 12:30 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > The BPF sideband information is tracked using a separate thread and
> > evlist.  But it's only useful for profiling kernel and we can skip it
> > when users profile their application only.
>
> nit: It may be worth noting that profiling an application implicitly
> excludes the kernel samples.
>
> > It seems it already fails to open the sideband event in that case.
> > Let's remove the noise in the verbose output anyway.
> >
> > Cc: Song Liu <song@...nel.org>
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>
> Reviewed-by: Ian Rogers <irogers@...gle.com>
>
> I wonder if the second evlist could be avoided similar to Howard's
> off-CPU sample events?
> I also wonder if we should make the evlist responsible for BPF and
> dummy/sideband events. Having unnecessary events increases the list
> size iterated over when creating sideband data, and so has a runtime
> cost. Having the logic separated in places like builtin-top and
> builtin-record feels suboptimal.

It appears we can indeed put this logic in evlist.

Thanks,
Song

> Thanks,
> Ian
>