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

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Date:   Tue, 21 Nov 2023 13:40:31 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Hector Martin <marcan@...can.st>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        James Clark <james.clark@....com>
Cc:     linux-perf-users@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Asahi Linux <asahi@...ts.linux.dev>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since v6.5

[Adding key people on Cc]

On Tue, 21 Nov 2023 12:08:48 +0000,
Hector Martin <marcan@...can.st> 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.

I can confirm that at least on 6.7-rc2, perf is pretty busted on any
asymmetric ARM platform. It isn't clear what criteria is used to pick
the PMU, but nothing works anymore.

The saving grace in my case is that Debian still ships a 6.1 perftool
package, but that's obviously not going to last.

I'm happy to test potential fixes.

	M.

-- 
Without deviation from the norm, progress is not possible.