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

["K.Prasad" <prasad@linux.vnet.ibm.com>]

On Sat, Sep 26, 2009 at 12:03:28PM -0400, Frank Ch. Eigler wrote:
> 
> Arjan van de Ven <arjan@infradead.org> writes:
> 
> > [...]
> > There are reasons for kernel code to ask for, and use, performance counters.
> > For example, in CPU freq governors this tends to be a good idea, but there
> > are other examples possible as well of course.
> > 
> > This patch adds the needed bits to do enable this functionality; they have been
> > tested in an experimental cpufreq driver that I'm working on, and the changes
> > are all that I needed to access counters properly.
> > [...]
> 
> 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.

Thanks,
K.Prasad