linux-kernel - Re: [PATCH] perf lock contention: Fix spinlock and rwlock accounting

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Message-ID: <ZtIv21BLm9BrU4CD@x1>
Date: Fri, 30 Aug 2024 17:47:23 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, 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, Song Liu <song@...nel.org>,
	bpf@...r.kernel.org, Xi Wang <xii@...gle.com>
Subject: Re: [PATCH] perf lock contention: Fix spinlock and rwlock accounting

On Fri, Aug 30, 2024 at 08:51:43AM -0700, Namhyung Kim wrote:
> Hi Arnaldo,
> 
> On Fri, Aug 30, 2024 at 6:23 AM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > On Tue, Aug 27, 2024 at 10:29:53PM -0700, Namhyung Kim wrote:
> > > The spinlock and rwlock use a single-element per-cpu array to track
> > > current locks due to performance reason.  But this means the key is
> > > always available and it cannot simply account lock stats in the array
> > > because some of them are invalid.
> > >
> > > In fact, the contention_end() program in the BPF invalidates the entry
> > > by setting the 'lock' value to 0 instead of deleting the entry for the
> > > hashmap.  So it should skip entries with the lock value of 0 in the
> > > account_end_timestamp().
> >
> > Thanks, applied to perf-tools-next,
> 
> I think this can go to perf-tools instead.

I think I published it already, don't think this is a major problem tho,
we can make a note when submitting for v6.12 that there are a few
patches that are already mainline.

For the future, its interesting that when posting patches we inform the
intended branch where it should be applied, something like:

[PATCH perf-tools] ...

Or I can add something to my scripts to check if the patch is a
regression introduced in the current merge window...

- Arnaldo