linux-kernel - Re: [PATCH] arm_pmu: Invert fallback armpmu

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Message-ID: <Y+43ghGB21FUm2ER@FVFF77S0Q05N.cambridge.arm.com>
Date:   Thu, 16 Feb 2023 14:02:42 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Janne Grunau <j@...nau.net>
Cc:     Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi Bangoria <ravi.bangoria@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        asahi@...ts.linux.dev
Subject: Re: [PATCH] arm_pmu: Invert fallback armpmu_filter() return value

Hi,

On Wed, Feb 15, 2023 at 12:27:13PM +0100, Janne Grunau wrote:
> Fixes a regression in "perf: Rewrite core context handling" for arm_pmu
> based drivers without a filter function pointer as the Apple M1 PMU.
> The event is ignored if filter() returns 'true' opposite to
> filter_match(). The refactoring failed to invert the return value if
> arm_pmu has no filter() function pointer of its own.
> 
> Fixes: bd2756811766 ("perf: Rewrite core context handling")
> Signed-off-by: Janne Grunau <j@...nau.net>

Thanks for the report and the patch, and apologies for this happening in the
first place; this has clearly slipped by our testing...

I think this fix is correct, but I spot that bd2756811766 also broken CHAIN
event filtering, and made armv8pmu_filter() trivial, so we can get rid of
arm_pmu::filter() entirely and make this simpler and clearer.

I'm going to send a couple of patches to addres both those issues in a moment,
with everyone here on Cc.

Thanks,
Mark.

> ---
>  drivers/perf/arm_pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 9b593f985805..9cb22f36cf66 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -556,7 +556,7 @@ static bool armpmu_filter(struct pmu *pmu, int cpu)
>  	if (ret && armpmu->filter)
>  		return armpmu->filter(pmu, cpu);
>  
> -	return ret;
> +	return !ret;
>  }
>  
>  static ssize_t cpus_show(struct device *dev,
> 
> ---
> base-commit: ceaa837f96adb69c0df0397937cd74991d5d821a
> change-id: 20230215-arm_pmu_m1_regression-b6dd48d0c792
> 
> Best regards,
> -- 
> Janne Grunau <j@...nau.net>
>