linux-kernel - Re: perf and cgroup event scheduling

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Date:	Thu, 31 Mar 2011 10:06:59 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: perf and cgroup event scheduling

Peter,

On Thu, Mar 31, 2011 at 6:27 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> Hi Stephane,
>
> while trying to make sense of various other fun event scheduling issues,
> I noticed that perf_cgroup_switch() isn't always doing the right thing.
>
> So we typically want to schedule: CPU-pinned, TASK-pinned, CPU-flexible
> TASK-flexible, however the current code doesn't respect that.
>
Unfortunately, you are right ;-). I think we should try to centralize
the scheduling
of per-cpu and per-thread event in a single function that goes through
the priority
list. In certain cases, we would sched out and back in per-thread
events, but that
would be the only to maintain the priority scheme. I will look into that.


In the meantime, yesterday, I found and fixed one potential kernel crash problem
related to mixing cgroup + per-thread events. I will be posting the
patch shortly.


> In particular perf_cgroup_sched_in() is placed wrong, it should be
> _before_ we schedule in the task contexts.
>
> There's further complications with things like perf_install_in_context()
> and perf_cgroup_move(), but those are either rare or 'interesting' to
> fix.
>
>
>
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