Messages in this thread | | | Date | Sat, 21 Aug 2010 11:30:36 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH 0/3] perf: show package power consumption in perf |
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > Right, short counters (like SH when not chained) need something to > > accumulate deltas into the larger u64. You can indeed use timers for > > that, hr or otherwise, but you don't need the swcounter hrtimer > > infrastructure for that. > > So what is the point in simulating a PMI using an hrtimer? It won't be > based on periods on the interesting counter but on time periods. This > is not how we want the samples. If we want timer based samples, we can > just launch a seperate software timer based event.
If we then measure the delta of the count during that constant-time period, we'll get a 'weight' to consider.
So for example if we sample with a period of every 1000 cache-misses, regular same-counter-PMU-IRQ sampling goes like this:
1000 1000 1000 1000 1000 ....
While if we use a hrtimer, we get variations:
1050 711 1539 2210 400
But using that variable period as a weight will, statistically, compensate for the variation.
It's similar to how the auto-freq code works - that too has variable periods (due to the self-adjustment) - which we compensate with weight.
Thanks,
Ingo
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