Subject: Re: [PATCH] perf: Allow set output buffer for tasks in the same
 thread group
From: Lin Ming <ming.m.lin@intel.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>, Arnaldo Carvalho de Melo <acme@infradead.org>,
        Tim Blechmann <tim@klingt.org>, David Ahern <dsahern@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
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	 <1303664726.20212.1.camel@twins>
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Date: Mon, 25 Apr 2011 21:40:38 +0800
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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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