linux-kernel - Re: [PATCH] perf/test: Skip leader sampling for s390

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Message-ID: <20250328182752.769662-1-ctshao@google.com>
Date: Fri, 28 Mar 2025 11:27:52 -0700
From: Chun-Tse Shao <ctshao@...gle.com>
To: tmricht@...ux.ibm.com
Cc: acme@...nel.org, agordeev@...ux.ibm.com, gor@...ux.ibm.com, 
	hca@...ux.ibm.com, irogers@...gle.com, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, linux-s390@...r.kernel.org, 
	namhyung@...nel.org, sumanthk@...ux.ibm.com, 
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf/test: Skip leader sampling for s390

We believe we know the problem, appreciate Stephan Eranian's investigation.
It comes from throttling. While the sampling is too high, the generic code
does not modify event scheduling. `perf_event_overflow()` simply returns 1,
and subsequently, `pmu_stop()` only stops the leader event, not the slave
events because the arch layer does not consider groups. Also, the
`event_stop()` callback only operates on a single event, not the siblings.

This would impact all architectures. Perhaps we can extend the
`evnet_stop()` callback to include a new argument to also stop the siblings.
We also welcome all suggestions and open to discuss any potential solutions.

Thanks,
CT

Cc: Stephane Eranian <eranian@...gle.com>