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    SubjectRe: [RFC][PATCH] perf_events: added new start/stop PMU callbacks
    On Mon, 2010-02-08 at 17:06 +0200, Stephane Eranian wrote:
    > In certain situations, the kernel may need to stop and start the
    > same event rapidly. The current PMU callbacks do not distinguish
    > between stop and release (i.e., stop + free the resource). Thus,
    > a counter may be released, then it will be immediately re-acquired.
    > Event scheduling will again take place with no guarantee to assign
    > the same counter. On some processors, this may event yield to failure
    > to assign the event back due to competion between cores.
    > This patch is adding a new pair of callback to stop and restart a
    > counter without actually release the underlying counter resource.
    > On stop, the counter is stopped, its values saved and that's it.
    > On start, the value is reloaded and counter is restarted (on x86,
    > actual restart is delayed until perf_enable()).
    > Note this patch does not provide support for non-X86 PMU. This needs
    > to be added.
    > Signed-off-by: Stephane Eranian <>
    > --

    I think we can do this much easier by adding a list_head to
    hw_perf_event and make event_list into a proper list, then we can remove
    that funny loop on remove and instead move the event to a remove_list
    when there's a put_event_constraint() method and iterate that list on

    But before we do that, I think we need to look at the /* hardware */
    part of struct hw_perf_event, and make that arch specific, we've been
    growing that a lot lately and I don't think !x86 uses any of that.

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      Last update: 2010-02-08 17:33    [W:0.020 / U:1.648 seconds]
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