linux-kernel - Re: [PATCH 1/3] perf: add context field to perf

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Date:	Tue, 12 Jul 2011 13:07:25 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joro@...tes.org>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Will Deacon <will.deacon@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	"acme@...stprotocols.net" <acme@...stprotocols.net>,
	Jason Wessel <jason.wessel@...driver.com>
Subject: Re: [PATCH 1/3] perf: add context field to perf_event

On 07/12/2011 01:03 PM, Joerg Roedel wrote:
> >  Regarding LWP - I thought the intent was self-profiling by the process
> >  for jits and the like?  If you also use it for perf, won't it be
> >  unusable for that?  Also, can't the process interfere, from userspace,
> >  by executing the unprivileged LWP instructions?
>
> Ingo made perf-integration a merge-requirement for LWP. It is not really
> well-suited for being integrated into perf because the design goal was
> easy and efficient self-profiling of tasks (like you stated). So
> integrating it into perf causes some pain. But lets see how it works
> out.

I don't think it's workable.  Having do_mmap() called in the task's 
context can change how it works.  And the task being able to kill/modify 
the profile, and not able to use LWP for itself, is a show stopper IMO.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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