Re: [PATCH v4 05/12] arm-cci: PMU: Add support for transactions

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 05/12] arm-cci: PMU: Add support for transactions
Date	2016-01-05 14:40 +0100
Message-ID	<qNA0a-3p1-1@gated-at.bofh.it> (permalink)
References	(3 earlier) <qH0sq-4lf-27@gated-at.bofh.it> <qH0LM-4tM-9@gated-at.bofh.it> <qH0Vs-4xe-9@gated-at.bofh.it> <qH1HP-55K-13@gated-at.bofh.it> <qNA0a-3p1-3@gated-at.bofh.it>
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On Mon, Dec 21, 2015 at 10:55:29AM +0000, Suzuki K. Poulose wrote:
> Thanks for that hint. Here is what I cam up with. We don't reschedule
> the events, all we need to do is group the writes to the counters. Hence
> we could as well add a flag for those events which need programming
> and perform the write in pmu::pmu_enable().

I'm still somewhat confused..

> Grouping the writes to counters can ammortise the cost of the operation
> on PMUs where it is expensive (e.g, CCI-500).

This rationale makes me think you want to reduce the number of counter
writes, not batch them per-se.

So why are you unconditionally writing all counters, instead of only
those that changed?
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Re: [PATCH v4 05/12] arm-cci: PMU: Add support for transactions Peter Zijlstra <peterz@infradead.org> - 2016-01-05 14:40 +0100
  Re: [PATCH v4 05/12] arm-cci: PMU: Add support for transactions "Suzuki K. Poulose" <Suzuki.Poulose@arm.com> - 2016-01-05 14:50 +0100
    Re: [PATCH v4 05/12] arm-cci: PMU: Add support for transactions Peter Zijlstra <peterz@infradead.org> - 2016-01-05 16:00 +0100

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