Messages in this thread | | | Date | Tue, 27 May 2008 09:40:35 -0700 | From | Arjan van de Ven <> | Subject | Re: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86 |
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On Tue, 27 May 2008 19:34:40 +0530 Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> wrote: > > What we are proposing is a scaled time value that is scaled to the > current CPU capacity. If the scaled utilisation is 50% when the CPU > is at 100% capacity, it is expected to remain at 50% even if the CPU's > capacity is dropped to 50%, while the traditional utilisation value > will be 100%.
When you use the word "capacity" I cringe ;(
> > The problem in the above two cases is that we had assumed that the > maximum CPU capacity is 100% at normal capacity (without IDA). > > If the CPU is at half the maximum frequency, then scaled stats should > show 50%.
see frequency != capacity. It's about more than frequency. It's about how much cache you have available too. If you run single threaded on a dual core cpu, you have 100% of the cache, but the cpu is 50% idle. But that doesn't mean that when you double the load, you actually get 2x the performance. So you're not at 50% of capacity!
> The point I am trying to make is whether scaling should be done > relative to CPUs designed maximum capacity or maximum capacity under > current constraints is to be discussed.
now you're back at "capacity".. we were at frequency before ;(
> > Case A: > ------ > > Scaled stats is stats relative to maximum designed capacity including > IDA
you don't know what that is though.
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