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

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Message-ID: <2025020426-spool-refreeze-2870@gregkh>
Date: Tue, 4 Feb 2025 11:16:03 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: 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>,
	"Liang, Kan" <kan.liang@...ux.intel.com>
Subject: Re: [PATCH] perf/core: move all of the pmu devices into their own
 location

On Tue, Feb 04, 2025 at 09:41:03AM +0200, Alexander Shishkin wrote:
> Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
> 
> > In sysfs, for some reason, all pmu devices seem to show up in the "root"
> > of /sys/devices/ making for a confusing mess as these devices are not
> > really at the root of the system at all.
> >
> > Create a fake root devices, "pmu_bus" and place them all under there if
> > they do not already have a parent device set, cleaning up sysfs to look
> > more sane.
> 
> Yeah, so what happens to the userspace that uses them via /sys/devices/*
> directly? Even I have scripts that do that.

You should never be doing that, as you have no idea what type of devices
are in that location in the tree.  You should be doing what the
documentation says to do, and look in /sys/bus/event_source/devices/
instead.  That didn't change here.

Again, system topology can, and will, change all the time in
/sys/devices/ so expect that.  The only "stable" locations are the
symlinks in the /sys/bus/ and /sys/class/ locations, which is why those
symlinks are present.

Been that way for over a decade now :)

thanks,

greg k-h