Messages in this thread | | | Date | Fri, 23 Apr 2010 07:26:02 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO |
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On Mon 2010-04-19 17:47:02, Arjan van de Ven wrote: > On Mon, 19 Apr 2010 16:29:39 +0100 > Tvrtko Ursulin <tvrtko.ursulin@sophos.com> wrote: > > > On Monday 19 Apr 2010 14:46:17 Arjan van de Ven wrote: > > > On Mon, 19 Apr 2010 10:09:55 +0100 > > > > Or in other words, does a pure IO workload benefit from now higher > > > > selected frequency? > > > > > > no. > > > Mixed workloads do. > > > but pure IO workloads also don't suffer since while idle, the > > > voltage goes down anyway. > > > > You mean that higher frequency does not have effect on power use if > > CPU is idle? Is that true for all/most processors? > > this is true for most processors that I'm aware of. > there's exceptions for things like where the idle time is really short,
Is not that exactly what will happen for 'cat /dev/<usb1>' case?
Plus I suspect that older cpus are slower at changing voltages, and slower at powering down when idle...
> > How and where in the code and how to enable that behaviour? From my > > experiments frequency goes down to minimum as soon as load goes away. > > What I was talking about is gradual lowering over a configurable > > period. It is not power efficient, but it could be good for latency > > in some workloads. > > it's not even good for that ;-( > > it's better then to stay high longer... at least on modern machines the > inbetween states are pretty much either useless or actually energy > hurting compared to the higher state.
So what about hiding those from ondemand on modern hw? Pavel
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