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Date: Thu, 26 Nov 2009 11:29:36 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Tejun Heo <tj@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>, linux-next@vger.kernel.org,
       linux-kernel@vger.kernel.org, Mike Galbraith <efault@gmx.de>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
       Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/4 tip/sched/core] sched: rename preempt_notifier to
 sched_notifier and always enable it
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* Tejun Heo <tj@kernel.org> wrote:

> Rename preempt_notifier to sched_notifier, move it from preempt.h to 
> sched.h, drop sched_ prefixes from ops names and make sched_notifier 
> always enabled.
> 
> This is to prepare for adding more notification hooks.  This patch 
> doesn't make any functional changes.

The sched notifiers and the various event notifiers we have in the same 
codepaths should really be unified into a single callback framework.

We have these _5_ callbacks:

...
        perf_event_task_sched_out(prev, next, cpu);
...
        fire_sched_out_notifiers(prev, next);
...
        trace_sched_switch(rq, prev, next);
...
        perf_event_task_sched_in(current, cpu_of(rq));
	fire_sched_in_notifiers(current);
...

That could be done with just two callbacks - one for sched-out, one for 
sched-in.

The best way to do that would be to use two TRACE_EVENT() callbacks, 
make them unconditional and register to them. (with wrappers to make it 
all convenient to use)

This requires some work but needs to be done.

	Ingo