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

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Message-ID: <20100506062855.GD1172@elte.hu>
Date:	Thu, 6 May 2010 08:28:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, 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


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Wed, May 05, 2010 at 08:16:36PM +0200, Peter Zijlstra wrote:
> > On Wed, 2010-05-05 at 20:15 +0200, Peter Zijlstra 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.
> > 
> > And again, I oppose mandating CONFIG_TRACEEVENT.
> 
> 
> And me too. But you don't need CONFIG_EVENT_TRACING for that. TRACE_EVENT() 
> with !CONFIG_EVENT_TRACING only produces tracepoints if CONFIG_TRACEPOINTS.
> 
> In fact, a first progress that would handle these compromizes would be to 
> have CONFIG_PERF_EVENT_SW.
> 
> For now perf_event_task_sched_in and perf_event_task_sched_out can stay as 
> is because they are perf core utils.
> 
> But all the rest (faults, migrations, etc..) could be tracepoints builtin 
> only if CONFIG_PERF_EVENT_SW. Which means CONFIG_PERF_EVENT_SW depends on 
> CONFIG_TRACEPOINTS.
> 
> But nobody is forced to build CONFIG_PERF_EVENT_SW, breakpoints don't need 
> it.

Yep. Also, most of the default distro kernels will have 3 sets of facilities:

 - preempt notifiers
 - tracepoints
 - sw events

which is crazy. We can just standardize on using the tracepoint interface 
definition methods - they are properly typed, widespread and well-known enough 
to be perfect for this.

( They are also under intense optimization - the jump-tracepoints patch makes 
  them probably even cheaper than preempt notifiers, in the off case. )

So lets get over this and consolidate our crazy hookery, and stand behind a 
single facility.

I'm also all for slimming down the trace events facilities by not requiring 
the /debug/tracing/ bits to be present.

	Ingo
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