linux-kernel - Re: [PATCH v4 07/10] perf tool_pmu: More accurately set the cpus for tool events

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Message-ID: <thuc2tb6vdrm2fbvcezmm6xqsvyjsy7rdafrcbksk73om364xc@sr4yd37i63go>
Date: Tue, 3 Feb 2026 18:27:26 -0500
From: Andres Freund <andres@...razel.de>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, "Dr. David Alan Gilbert" <linux@...blig.org>, 
	Yang Li <yang.lee@...ux.alibaba.com>, James Clark <james.clark@...aro.org>, 
	Thomas Falcon <thomas.falcon@...el.com>, Thomas Richter <tmricht@...ux.ibm.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH v4 07/10] perf tool_pmu: More accurately set the cpus for
 tool events

Hi,

On 2026-02-03 15:05:39 -0800, Ian Rogers wrote:
> Thanks for the bug report! There were changes in v6.19 to change how
> metrics were computed hence the fault in the metric computation. The
> bisected patch is at fault, it aims to compute the CPU maps for tool
> events in a way to avoid unnecessary sched setaffinity calls. By
> having a smaller CPU map it set up a situation with user CPUs where
> the tool events could have no CPUs, removed from the list of events
> and the later seg fault occurred.

Thanks for the quick reply!

> I sent out a new patch series:
> https://lore.kernel.org/linux-perf-users/20260203225129.4077140-1-irogers@google.com/
> that has a revert of this patch, a fix to correctly avoid the segfault in
> the prepare_metric function, and a new patch to properly reduce the CPU maps
> of the tool events. The remaining affinity reduction patches are still part
> of the series and I believe ready to land.

That sounds like it's targeted for 6.20?  I assume the revert on its own needs
to land in 6.19 (or stable if too late for 6.19) somehow?

Greetings,

Andres Freund