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SubjectRe: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters

* Arjan van de Ven <arjan@infradead.org> wrote:

> On Sun, 27 Sep 2009 00:02:46 +0530
> "K.Prasad" <prasad@linux.vnet.ibm.com> wrote:
>
> > On Sat, Sep 26, 2009 at 12:03:28PM -0400, Frank Ch. Eigler wrote:
>
> > > For what it's worth, this sort of thing also looks useful from
> > > systemtap's point of view.
> >
> > Wouldn't SystemTap be another user that desires support for
> > multiple/all CPU perf-counters (apart from hw-breakpoints as a
> > potential user)? As Arjan pointed out, perf's present design would
> > support only a per-CPU or per-task counter; not both.
>
> I'm sorry but I think I am missing your point. "all cpu counters"
> would be one small helper wrapper away, a helper I'm sure the
> SystemTap people are happy to submit as part of their patch series
> when they submit SystemTap to the kernel.

Yes, and Frederic wrote that wrapper already for the hw-breakpoints
patches. It's a non-issue and does not affect the design - we can always
gang up an array of per cpu perf events, it's a straightforward use of
the existing design.

User-space tools have been doing this for ages already, 'perf top' will
open an array of per cpu events to monitor all events in the system.

Ingo


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