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

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Message-ID: <9656a86c-30fb-48d9-9327-920cd449e73a@linux.intel.com>
Date: Tue, 4 Feb 2025 13:23:51 -0500
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: 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 2025-02-04 11:28 a.m., Greg Kroah-Hartman wrote:
> On Tue, Feb 04, 2025 at 09:06:18AM -0500, Liang, Kan wrote:
>>
>>
>> On 2025-02-04 5:16 a.m., Greg Kroah-Hartman wrote:
>>> 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.
>>>
>>
>> Not just the script, the /sys/devices/ is also used in the current perf
>> tool. For example,
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/util/mem-events.c#n192
>>
>> And the comments and document in the perf tool.
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/util/pmu.c#n39
> 
> Note, this file looks to work properly, it's just the comment that is
> incorrect.
> 
> Any hints on what perf command or test I should run to verify I did get
> this all right?

For the perf tool, "perf test" should be run at minimum.

> 
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/Documentation/perf-list.txt#n191
> 
> I'll fix that.
> 
>> I think it should bring big impact for the end user, especially when
>> they still use an older perf tool and script.
> 
> It seems that the majority of the perf code IS looking in the correct
> place, just mem-events.c seemed wrong.
> 

There should be two more.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/builtin-stat.c#n100

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/x86/util/iostat.c#n35

Thanks,
Kan