linux-kernel - Re: [PATCH] perf: Allow set output buffer for tasks in the same thread group

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Date:	Mon, 25 Apr 2011 21:40:38 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tim Blechmann <tim@...ngt.org>,
	David Ahern <dsahern@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf: Allow set output buffer for tasks in the same
 thread group

On Mon, 2011-04-25 at 01:05 +0800, Peter Zijlstra wrote:
> On Sun, 2011-04-24 at 22:57 +0800, Lin Ming wrote:
> > Currently, kernel only allows an event to redirect its output to other
> > events of the same task.
> > 
> > This causes PERF_EVENT_IOC_SET_OUTPUT ioctl fails when an event is
> > trying to redirect its output to other events in the same thread group.
> 
> Which is exactly what it should do, you should never be allowed to
> redirect your events to that of another task, since that other task
> might be running on another CPU.
> 
> The buffer code strictly assumes no concurrency, therefore its either
> one task or one CPU.

Well, this is not the right fix, then the perf tool code need to be
fixed.


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