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Message-ID: <20100506082714.GA2036@elte.hu>
Date: Thu, 6 May 2010 10:27:14 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Tejun Heo <tj@...nel.org>
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
* Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On 05/06/2010 08:28 AM, Ingo Molnar wrote:
> > ( They are also under intense optimization - the jump-tracepoints patch makes
> > them probably even cheaper than preempt notifiers, in the off case. )
>
> I mostly agree on other points but TPs and sched_notifiers are inherently
> different in how they are enabled/disabled. sched_notifiers are
> enabled/disabled per-task and at least w/ cmwq, there will always be some
> tasks with active sched_notifiers so code level optimizations aren't really
> useful.
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.
Preempt notifiers are for things like KVM which want to do extended context
saving. They are _NOT_ 'hooks' into the scheduler.
Ingo
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