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SubjectRe: [RFC] [PATCH 1/1] perf: add support for arch-dependent symbolic event names to "perf stat"

* Paul Mackerras <paulus@samba.org> wrote:

> On Thu, Mar 11, 2010 at 01:46:08PM +0100, Ingo Molnar wrote:
> >
> > * Corey Ashford <cjashfor@linux.vnet.ibm.com> wrote:
> >
> > > On 3/3/2010 6:30 PM, Corey Ashford wrote:
> > > >For your review, this patch adds support for arch-dependent symbolic
> > > >event names to the "perf stat" tool, and could be expanded to other
> > > >"perf *" commands fairly easily, I suspect.
>
> > I'm quite much against stop-gap measures like this - they tend to become
> > tomorrow's impossible-to-remove quirk.
> >
> > If you want extensible events you can already do it by providing an ftrace
> > tracepoint event via TRACE_EVENT. They are easy to add and ad-hoc, and are
> > supported throughout by perf.
>
> If I've understood correctly what Corey is doing, I think you're missing the
> point. The idea, I thought, was to provide a way to be able to use symbolic
> names for raw hardware events rather than just numbers. I don't see how
> ftrace tracepoint events are relevant to that.

tracepoints are relevant because they are the currently best way of how we
assign symbolic names to various kernel-internal events. For ad-hoc usecases
like this:

http://dri.freedesktop.org/wiki/IntelPerformanceTuning

I'd much rather see that facility used (and, to the extent needed, extended)
to provide support for rare arch events that we dont want to enumerate in a
generic way.

Or, if the events are important enough to be hardcoded into the perf ABI
itself, they should be generalized in a meaningful way - even if you dont
expect them to show up on other CPUs.

Ingo


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