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

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Message-ID: <20110712100354.GC29812@8bytes.org>
Date:	Tue, 12 Jul 2011 12:03:54 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Avi Kivity <avi@...hat.com>
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 Tue, Jul 12, 2011 at 12:55:25PM +0300, Avi Kivity wrote:

> Have a helper kernel thread do it for you.  Or extend use_mm() to return
> the old mm (without dropping its refcount) and add a way to restore it.

Making use_mm usable for regular tasks too sounds like a good idea.
Thanks.

> 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.

	Joerg

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