linux-kernel - Re: [PATCH] perf record/arm-spe: Override attr->sample

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Message-ID: <35a4f70f-d7ef-6e3c-dc79-aa09d87f0271@arm.com>
Date:   Mon, 17 Jan 2022 10:27:11 +0000
From:   German Gomez <german.gomez@....com>
To:     James Clark <james.clark@....com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Cc:     Chase Conklin <chase.conklin@....com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Stephane Eranian <eranian@...gle.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, "acme@...nel.org" <acme@...nel.org>
Subject: Re: [PATCH] perf record/arm-spe: Override attr->sample_period for
 non-libpfm4 events

Hi James,

On 17/01/2022 09:59, James Clark wrote:
>
> On 14/01/2022 21:21, German Gomez wrote:
>> A previous commit preventing attr->sample_period values from being
>> overridden in pfm events changed a related behaviour in arm_spe.
>>
>> Before this patch:
>> perf record -c 10000 -e arm_spe_0// -- sleep 1
>>
>> Would not yield an SPE event with period=10000, because the arm-spe code
> Just to clarify, this seems like it should say "Would yield", not "Would not yield",
> as in it was previously working?

"this patch" refers to the patch I'm sending, not the one it's fixing.
I might have to rewrite this to make it more clear. How about:

===
A previous patch preventing "attr->sample_period" values from being
overridden in pfm events changed a related behaviour in arm-spe.

Before said patch:
perf record -c 10000 -e arm_spe_0// -- sleep 1

Would yield an SPE event with period=10000. After the patch, the period
in "-c 10000" was being ignored because the arm-spe code initializes
sample_period to a non-zero value.

This patch restores the previous behaviour for non-libpfm4 events.
===

Thanks for the review,
German