linux-kernel - Re: [RFC PATCHSET] sched,perf: unify tracers in sched and move perf on top of TP

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Date:	Wed, 05 May 2010 15:09:14 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Avi Kivity <avi@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>, mingo@...e.hu,
	efault@....de, paulus@...ba.org, acme@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCHSET] sched,perf: unify tracers in sched and move perf
 on top of TP

Hello,

On 05/05/2010 02:33 PM, Avi Kivity wrote:
> On 05/05/2010 02:38 PM, Peter Zijlstra wrote:
>> As it stands I'd argue to simply drop this whole idea. The SCHED_EVENT()
>> thing doesn't look like its worth the obfuscation and I'm very much
>> opposed to making perf and sched_notifiers rely on tracepoints.
> 
> We can make perf rely on sched_notifiers, I think it's exactly the same
> case as kvm - extra cpu state that needs switching at context switch
> time.  We could also make fpu switching use sched_notifiers, but that's
> pushing it a bit.

Oh, that was my first attempt too.  The difference between TPs and
sched_notifiers is the enable condition.  TP is system-wide while
sched_notifier is per-task.  The thing is that for perf hooks,
system-wide enable condition works much better.  Also, w/
sched_notifiers, there's the problem that no one else but self can
enable/disable it (which can be changed but doing it without causing
call time overhead requires a bit of effort).

Thanks.

-- 
tejun
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