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

[Peter Zijlstra]

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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