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    SubjectRe: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters
    On Sat, Sep 26, 2009 at 12:03:28PM -0400, Frank Ch. Eigler wrote:
    > Arjan van de Ven <> 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.


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