Re: [RFC PATCHSET] sched,perf: unify tracers in sched and move perf on top of TP

Ingo Molnar
2010-05-06T08:27:48Z

* Tejun Heo <tj@kernel.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