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

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Message-ID: <4E1C0F02.9040906@redhat.com>
Date:	Tue, 12 Jul 2011 12:08:18 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	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 11:38 AM, Peter Zijlstra wrote:
> On Tue, 2011-07-12 at 10:20 +0300, Avi Kivity wrote:
>
> >  Maybe we need a generic "run this function in this task's context"
> >  mechanism instead.  Like an IPI, but targeting tasks instead of cpus.
> >
>
> kernel/event/core.c:task_function_call() like?

Similar, but with stronger guarantees: when the function is called, 
current == p, and the task was either sleeping or in userspace.

This can be used to reduce synchronization requirements between tasks.  
For example, you can set a task-local bit flag with this, without 
atomics.  If this is rare enough, it's a net win compared to adding atomics.

aio completions might also make use of this.

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

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