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

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Message-ID: <4BE280AA.6020304@kernel.org>
Date:	Thu, 06 May 2010 10:41:14 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>, efault@....de,
	avi@...hat.com, 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, Ingo.

On 05/06/2010 10:27 AM, Ingo Molnar wrote:
> Note that preempt notifiers used to modify scheduling behavior/semantics i'm 
> really against. Please get that functionality into the scheduler - especially 
> if it's essentially always-on.

Okay.  Well, cmwq's usage of it isn't that hairy.  It's used for two
things.

1. to count the number of currently running workers which I think is
   fine for such hooks.

2. to wake up another worker.  I don't think this falls in the
   category of "behavior/semantics" change.  It just does
   try_to_wake_up() with the only caveat being it's called under the
   rq lock so requires a different API.  There's nothing which alters
   the scheduler behavior in any pervasive way.  It just looks at the
   counter and wakes up another task if the condition is right
   *before* beginning any of real scheduling work.

But, anyways, making a dedicated fixed function calls certainly isn't
a problem and might as well be slightly cheaper as it's always gonna
be there anyway.  If that's preferred, I'll happily take that path.

Thanks.

-- 
tejun
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