linux-kernel - Re: [PATCH v3 2/2] perf bpf-filter: Enable events manually

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Message-ID: <1094385e-6f86-453f-a48e-fa284dcae385@linux.ibm.com>
Date: Wed, 6 Aug 2025 11:29:24 +0200
From: Thomas Richter <tmricht@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>, bpf@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v3 2/2] perf bpf-filter: Enable events manually

On 8/5/25 16:14, Alexander Gordeev wrote:
> On Tue, Aug 05, 2025 at 02:54:05PM +0200, Ilya Leoshkevich wrote:
> 
> Hi Thomas,
> 
> The below comments date to the initial version, so the question is
> rather to you:
> 
>> On linux-next
> 
> This line is extra.

I just wanted to let readers know which repo to look at.

> 
>> commit b4c658d4d63d61 ("perf target: Remove uid from target")
>> introduces a regression on s390. In fact the regression exists
>> on all platforms when the event supports auxiliary data gathering.
> 
> So which commit it actually fixes: the above, the below or the both?
> 
>> Fixes: 63f2f5ee856ba ("libbpf: add ability to attach/detach BPF program to perf event")
> 
> Thanks!
> 

Good question!  Pick what you like... :-)

The issue in question originates from a patch set of 10 patches.
The patch set rebuilds event sample with filtering and migrates
from perf tool's selective process picking to more generic eBPF
filtering using eBPF programs hooked to perf events.

To be precise, the issue Ilya's  patch fixes is this:
Fixes: 63f2f5ee856ba ("libbpf: add ability to attach/detach BPF program to perf event")

However the issue (perf failure) does *NOT* show up until this patch is applied:
commit b4c658d4d63d61 ("perf target: Remove uid from target")

There are some patches in between the two (when you look at the complete patch set),
but they do not affect the result.

Hope that helps.
-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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