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

Ingo Molnar
2010-05-06T06:29:10Z

* Frederic Weisbecker <fweisbec@gmail.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