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

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Message-ID: <2025020444-savage-latrine-0c31@gregkh>
Date: Tue, 4 Feb 2025 19:03:30 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Stephane Eranian <eranian@...gle.com>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	"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 04, 2025 at 09:49:55AM -0800, Ian Rogers wrote:
> 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.

Nope, all that has to happen is this line:
	snprintf(buf, PATH_MAX, "/sys/devices/%s/events/%s", e->pmu ? e->pmu : "cpu", e->name);
be changed to:
	snprintf(buf, PATH_MAX, "/sys/bus/event_source/devices/%s/events/%s", e->pmu ? e->pmu : "cpu", e->name);


thanks,

greg k-h