Re: [PATCH 1/4 tip/sched/core] sched: rename preempt_notifier to sched_notifier and always enable it

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2009-11-26 at 11:29 +0100, Ingo Molnar wrote:
> * 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.

Ugh,.. it also makes TRACE_EVENT unconditional.

That really wants a separate option.. What we could do is take regular
notifier lists and extend them to auto-generate a tracepoint when the
trace stuff is enabled or something.