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

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Message-ID: <20100506071153.GA3626@elte.hu>
Date:	Thu, 6 May 2010 09:11:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tejun Heo <tj@...nel.org>, efault@....de, avi@...hat.com,
	paulus@...ba.org, acme@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCHSET] sched,perf: unify tracers in sched and move perf
 on top of TP


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, 2010-05-06 at 08:31 +0200, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > Well, I'd much rather just see a direct call in the code than having to 
> > > reverse engineer wth hangs onto that _EVENT() junk.
> > 
> > Direct calls into code were fine 10 years ago, but since then we got:
> > 
> >  - preempt notifiers
> 
> Are per task an no good for driving perf.

No, but they could be expressed via tracepoints.

> >  - sw events
> >  - tracepoints
> 
> Are unrelated to the core perf scheduler calls.

Still they pose 3 different types of callback regimes, all for a slightly 
different purpose.

> > Which add up to a lot more than just a plain call into code.
> > 
> > Also, with the jump-optimizations we will have tracepoints that are 
> > _cheaper_ than a plain function call.
> 
> Which can just as easily be used on the core perf hooks.
> 
> > > Also, we don't need ABI muck for this.
> > 
> > we already have an ABIs in place here - this would just properly unify and 
> > enumerate it.
> 
> I'm not getting it, this is about in-kernel stuff, there are _NO_ in kernel 
> ABIs.

Yes - but the callbacks i mentioned do include ABIs, such as the sw event 
callbacks.

So my point is to have one coherent callback mechanism for it.

That said, i agree with you that turning the basic perf scheduling calls into 
events goes one step too far. But all the _other_ 3 types of callbacks (and we 
might as well add a fourth type as well: the butt-ugly hotplug event notifier 
chains) should be consolidated really.

	Ingo
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