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

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Message-ID: <2025020507-anteater-icy-44ab@gregkh>
Date: Wed, 5 Feb 2025 06:41:23 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Ian Rogers <irogers@...gle.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>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	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 10:17:17AM -0800, Ian Rogers wrote:
> On Mon, Feb 3, 2025 at 11:05 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, Feb 03, 2025 at 11:44:13AM -0800, Ian Rogers wrote:
> > > On Mon, Feb 3, 2025 at 11:25 AM Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> [snip]
> > > > Note, if you all don't like "pmu_bus" for the name, that's fine, please
> > > > let me know and I can rename it to something else, but it should be
> > > > something to get these objects out of the root sysfs directory.
> > >
> > > Excuse my ignorance, does the event_source bus already provide a
> > > similar solution?
> > > ```
> > > $ ls /sys/bus/event_source/devices
> > > breakpoint   i915       msr         uncore_arb     uncore_cbox_3
> > > uncore_cbox_7              uprobe
> > > cpu          intel_bts  power       uncore_cbox_0  uncore_cbox_4  uncore_clock
> > > cstate_core  intel_pt   software    uncore_cbox_1  uncore_cbox_5
> > > uncore_imc_free_running_0
> > > cstate_pkg   kprobe     tracepoint  uncore_cbox_2  uncore_cbox_6
> > > uncore_imc_free_running_1
> > > $ ls /sys/devices
> > > breakpoint   intel_pt     platform    uncore_arb     uncore_cbox_5
> > >          uprobe
> > > cpu          isa          pnp0        uncore_cbox_0  uncore_cbox_6
> > >          virtual
> > > cstate_core  kprobe       power       uncore_cbox_1  uncore_cbox_7
> > > cstate_pkg   LNXSYSTM:00  software    uncore_cbox_2  uncore_clock
> > > i915         msr          system      uncore_cbox_3  uncore_imc_free_running_0
> > > intel_bts    pci0000:00   tracepoint  uncore_cbox_4  uncore_imc_free_running_1
> > > ```
> >
> > Those are the exact same device structures :)
> >
> > Look at /sys/bus/event_source/devices/ those are symlinks back to
> > /sys/devices.  In other words, that's the exact same structures, and
> > the mess in /sys/devices/ with these event devices is what I am trying
> > to clean up.
> 
> Thanks! Again my ignorance, why do we need pmu_bus?

You need some sort of "bus" to group all of your devices on.  It could
also be a class, your call.  This is how the driver model in the kernel
works.

> Could the symlinks in event_source be the actual devices?

That's not how the driver model works.

> Perhaps for temporary compatibility some symlinks could be placed in
> /sys/devices?

No, /sys/devices/ is never guaranteed to have stable placement.

And define "temporary" :)

thanks,

greg k-h