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

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Message-ID: <ZV1AnNB2CSbAUFVg@archie.me>
Date:   Wed, 22 Nov 2023 06:43:24 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Hector Martin <marcan@...can.st>,
        Linux perf Profiling <linux-perf-users@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     Marc Zyngier <maz@...nel.org>,
        Asahi Linux Mailing List <asahi@...ts.linux.dev>,
        Ian Rogers <irogers@...gle.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since
 v6.5

On Tue, Nov 21, 2023 at 09:08:48PM +0900, Hector Martin wrote:
> Perf broke on all Apple ARM64 systems (tested almost everything), and
> according to maz also on Juno (so, probably all big.LITTLE) since v6.5.
> 
> Test command:
> 
> sudo taskset -c 0 ./perf stat -e apple_icestorm_pmu/cycles/ -e
> apple_firestorm_pmu/cycles/ -e cycles ls
> 
> Since this is taskset to CPU #0 (LITTLE core, icestorm), only events for
> icestorm are expected.
> 
> I bisected the breakage to two distinct points:
> 
> 5ea8f2ccffb is the first bad commit. With its parent, the output is as
> expected (same as v6.4):
> 
>          3,297,462      apple_icestorm_pmu/cycles/
> 
>      <not counted>      apple_firestorm_pmu/cycles/
>                        (0.00%)
>      <not counted>      cycles
>                        (0.00%)
> 
> With 5ea8f2ccffb everything breaks:
> 
>    <not supported>      apple_icestorm_pmu/cycles/
> 
>    <not supported>      apple_firestorm_pmu/cycles/
> 
>      <not counted>      cycles
>                        (0.00%)
> 
> Somewhere along the way to 82fe2e45cdb00 things get even worse (didn't
> bother bisecting this range). With its parent:
> 
>    <not supported>      apple_icestorm_pmu/cycles/
> 
>    <not supported>      apple_firestorm_pmu/cycles/
> 
>    <not supported>      apple_icestorm_pmu/cycles/
> 
>    <not supported>      apple_firestorm_pmu/cycles/
> 
> Then 82fe2e45cdb00 leads to the current v6.5 behavior:
> 
>      <not counted>      apple_icestorm_pmu/cycles/
>                        (0.00%)
>      <not counted>      apple_firestorm_pmu/cycles/
>                        (0.00%)
>      <not counted>      cycles
>                        (0.00%)
> 
> If I taskset the task to CPU#2 (big core, firestorm), I get events:
> 
>          1,454,858      apple_icestorm_pmu/cycles/
> 
>          1,454,760      apple_firestorm_pmu/cycles/
> 
>          1,454,384      cycles
> 
> 
> So the current behavior is that all output seems to come from the
> firestorm PMU event counter, regardless of requested event.
> 
> This is all unchanged and still broken in v6.7-rc2.
> 

Thanks for the regression report (and it has been handled well already).
I'm adding it to regzbot for tracking:

#regzbot ^introduced: 5ea8f2ccffb239

-- 
An old man doll... just what I always wanted! - Clara

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