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SubjectRe: [RFC][PATCH] perf_events: added new start/stop PMU callbacks
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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 <eranian@google.com>
> --

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
hw_perf_enable().

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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