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Date: Fri, 27 Nov 2009 14:33:22 +1100
From: Paul Mackerras <paulus@samba.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Tejun Heo <tj@kernel.org>, 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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Ingo Molnar writes:

> 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)

I'd rather 5 explicit direct function calls than two direct calls and
five indirect function calls, actually...

Paul.