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

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Message-ID: <2025020544-shakily-flattered-93b7@gregkh>
Date: Wed, 5 Feb 2025 19:45:07 +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 Wed, Feb 05, 2025 at 08:48:21AM -0800, Ian Rogers wrote:
> On Tue, Feb 4, 2025 at 9:41 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > 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.
> 
> Sure, I wasn't clear how this mapped out in sysfs.
> 
> > > Could the symlinks in event_source be the actual devices?
> >
> > That's not how the driver model works.
> 
> Ok, so I guess that's what's confusing me. Where will the new devices
> be in sysfs? If it is /sys/bus/pmu_bus then why is
> /sys/bus/event_source a different case? I guess I should read docs and
> the source :-)

Look at what is in /sys/bus/event_source/devices/ today.  That's a bunch
of symlinks to where in /sys/devices/ the devices are located.

I just moved all of the pmu bus devices under /sys/devices/pmu_bus/
instead of them showing up in the root at /sys/devices/ as that's not
where a bus should be placing individual devices like this.

thanks,

greg k-h