linux-kernel - Re: [PATCH] perf/core: move all of the pmu devices into their own location

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Message-ID: <CAP-5=fWT5J0svFsA-jqvE4P=NnTdrsKPF9x6JHkUEDp-vBd_1w@mail.gmail.com>
Date: Tue, 4 Feb 2025 09:49:55 -0800
From: Ian Rogers <irogers@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Stephane Eranian <eranian@...gle.com>, 
	Vince Weaver <vincent.weaver@...ne.edu>
Cc: "Liang, Kan" <kan.liang@...ux.intel.com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] perf/core: move all of the pmu devices into their own location

On Tue, Feb 4, 2025 at 9:12 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Tue, Feb 04, 2025 at 11:41:38AM -0500, Vince Weaver wrote:
> > On Tue, 4 Feb 2025, Greg Kroah-Hartman wrote:
> >
> > >
> > > It seems that the majority of the perf code IS looking in the correct
> > > place, just mem-events.c seemed wrong.
> >
> > I hate to tell you, but other places in userspace are depending on the
> > current setup.  libpfm4, used by PAPI, is looking directly in /sys/devices
> > for pmus and will break with the changes you are planning.
>
> Then that too needs to be fixed, sorry.  Again, devices can, and will,
> move around in /sys/devices/ you can never hard-code any paths there.
> Any userspace code must ALWAYS be able to handle that, that's a sysfs
> requirement.
>
> And do you have a link to the source for that code?  Good news is that
> if the code is fixed in userspace, it will work for any kernel (old or
> new).

+Stephane Eranian

I see use of /sys/devices in at least:
https://sourceforge.net/p/perfmon2/libpfm4/ci/master/tree/lib/pfmlib_perf_event_pmu.c
I imagine it isn't a big job to clean it up.

Thanks,
Ian