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

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Message-ID: <2025020447-gyration-wireless-f7da@gregkh>
Date: Tue, 4 Feb 2025 18:12:07 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: 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>,
	Ian Rogers <irogers@...gle.com>,
	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 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).

thanks,

greg k-h