linux-kernel - Re: [PATCH 1/4 tip/sched/core] sched: rename preempt_notifier to sched

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Date:	Fri, 27 Nov 2009 05:54:59 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Tejun Heo <tj@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/4 tip/sched/core] sched: rename preempt_notifier to
 sched_notifier and always enable it


* Paul Mackerras <paulus@...ba.org> wrote:

> 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...

Those five callbacks are typically disabled on a regular Linux system. 
So i'd rather have two sites with some NOPs in them. (no branches, no 
calls)

	Ingo
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