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References: <20220322120834.98637-1-zhouchengming@bytedance.com>
 <20220322120834.98637-3-zhouchengming@bytedance.com> <YjnIpn/PCM6wKpOC@hirez.programming.kicks-ass.net>
In-Reply-To: <YjnIpn/PCM6wKpOC@hirez.programming.kicks-ass.net>
From:   Namhyung Kim <namhyung@kernel.org>
Date:   Tue, 22 Mar 2022 15:21:51 -0700
Message-ID: <CAM9d7cju-Z0_+WuhCZ+Y-4Hm6MCmXbF6XVBGd-n8BP_yoici5Q@mail.gmail.com>
Subject: Re: [PATCH v2 2/6] perf/core: Introduce percpu perf_cgroup
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Chengming Zhou <zhouchengming@bytedance.com>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Stephane Eranian <eranian@google.com>,
        linux-perf-users <linux-perf-users@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        duanxiongchun@bytedance.com, songmuchun@bytedance.com
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On Tue, Mar 22, 2022 at 6:01 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> 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 ?

I think it's supported from the beginning by writing PID to a file
in the cgroupfs.

Thanks,
Namhyung