Messages in this thread | | | Subject | Re: [PATCHv3 5/5] arm-cci: CCI-500: Work around PMU counter writes | From | "Suzuki K. Poulose" <> | Date | Fri, 11 Dec 2015 11:28:45 +0000 |
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On 10/12/15 15:42, Mark Rutland wrote: > On Tue, Nov 17, 2015 at 06:03:27PM +0000, Suzuki K. Poulose wrote: >> The CCI PMU driver sets the event counter to the half of the maximum >> value(2^31) it can count before we start the counters via >> pmu_event_set_period(). This is done to give us the best chance to >> handle the overflow interrupt, taking care of extreme interrupt latencies.
> > This should work, but it seems very heavyweight given we do it for each > write. > > Can we not amortize this by using the {start,commit,cancel}_txn hooks? > > Either we can handle 1-4 and 6-8 in those, or we can copy everything > into a shadow state and apply it all in one go at commit_txn time.
I took a look at it. The only worrying part is, if pmu->add() will be called outside *_txn().
from linux/perf_event.h:
/* * Adds/Removes a counter to/from the PMU, can be done inside a * transaction, see the ->*_txn() methods. *
As of now it is only called within the transactions, but the comment somehow doesn't look like enforces it.
Thoughts ?
Suzuki
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