linux-kernel - Re: [PATCH v2 2/6] perf/core: Introduce percpu perf

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Message-ID: <YjnIpn/PCM6wKpOC@hirez.programming.kicks-ass.net>
Date:   Tue, 22 Mar 2022 14:01:26 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, eranian@...gle.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        duanxiongchun@...edance.com, songmuchun@...edance.com
Subject: Re: [PATCH v2 2/6] perf/core: Introduce percpu perf_cgroup

On Tue, Mar 22, 2022 at 08:08:30PM +0800, Chengming Zhou wrote:
> Although we don't have incosistency problem any more, we can
> have other problem like:
> 
> CPU1					CPU2
> (in context_switch)			(attach running task)
> 					prev->cgroups = cgrp2
> perf_cgroup_sched_switch(prev, next)
> 	cgrp2 == cgrp2 is True
> 

Again, I'm not following, how can you attach to a running task from
another CPU ?