linux-kernel - Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since v6.5

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Message-ID: <88cea92d-98ee-4a1e-8a44-a7c6a247ba2e@linaro.org>
Date: Fri, 16 Aug 2024 09:57:39 +0100
From: James Clark <james.clark@...aro.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Thorsten Leemhuis <regressions@...mhuis.info>,
 Arnaldo Carvalho de Melo <acme@...hat.com>, Ian Rogers <irogers@...gle.com>,
 Mark Rutland <mark.rutland@....com>,
 Linux perf Profiling <linux-perf-users@...r.kernel.org>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 James Clark <james.clark@....com>, "cc: Marc Zyngier" <maz@...nel.org>,
 Hector Martin <marcan@...can.st>, Asahi Linux <asahi@...ts.linux.dev>,
 Linux regressions mailing list <regressions@...ts.linux.dev>
Subject: Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since
 v6.5



On 15/08/2024 4:53 pm, Arnaldo Carvalho de Melo wrote:
> On Thu, Aug 15, 2024 at 12:27:21PM -0300, Arnaldo Carvalho de Melo wrote:
>> On Thu, Aug 15, 2024 at 04:15:41PM +0100, James Clark wrote:
>>> In one of your investigations here
>>> https://lore.kernel.org/lkml/Zld3dlJHjFMFG02v@x1/ comparing "cycles",
>>> "cpu-cycles" and "cpu_cycles" events on Arm you say only some of them open
>>> events on both core types. I wasn't able to reproduce that on
>>> perf-tools-next (27ac597c0e) or v6.9 (a38297e3fb) for perf record or stat. I
>>> guessed the 6.9 tag because you only mentioned it was on tip and it was 29th
>>> May. For me they all open exactly the same two legacy events with the
>>> extended type ID set.
>>>
>>> It looks like the behavior you see would be caused by either missing this
>>> kernel change:
>>>
>>>    5c81672865 ("arm_pmu: Add PERF_PMU_CAP_EXTENDED_HW_TYPE capability")
>>>     (v6.6 release)
> 
> What I have now is:
> 
> 6.1.92-15907-gf36fd2695db3
> 
> It was a bit older, but 6.1 ish as well, I'll try to either get a new
> kernel from Libre Computer or build one myself.
> 
> - Arnaldo
>

Thanks for the confirmation. In that case you may not even need to 
retest. I was only wondering if it was broken from v6.6 onwards, but 6.1 
not working is expected. And I'm certain that you'll find any later 
versions working.

>>> Or this userspace change, but unlikely as it was a fix for Apple M hardware:
>>>
>>>    25412c036 ("perf print-events: make is_event_supported() more robust")
>>>     (v6.9 release)
>>>
>>> Do you remember if you were using a new kernel or only testing a new Perf?
>>
>> I normally use the distro/SoC provided kernel, didn't I add the 'uname
>> -a' output in those investigations (/me slaps himself in the face
>> speculatively...)?