Messages in this thread | | | Date | Fri, 21 Jun 2013 14:34:00 -0700 | From | Arjan van de Ven <> | Subject | Re: power-efficient scheduling design |
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On 6/21/2013 2:23 PM, Catalin Marinas wrote: >> >> oops sorry I misread your mail (lack of early coffee I suppose) >> >> I can see your point of having a thing for "did we ask for all the performance >> we could ask for" prior to doing a load balance (although, for power efficiency, >> if you have two tasks that could run in parallel, it's usually better to >> run them in parallel... so likely we should balance anyway) > > Not necessarily, especially if parallel running implies powering up a > full cluster just for one CPU (it depends on the hardware but for > example a cluster may not be able to go in deeper sleep states unless > all the CPUs in that cluster are idle).
I guess it depends on the system
the very first cpu needs to power on * the core itself * the "cluster" that you mention * the memory controller * the memory (out of self refresh)
while the second cpu needs * the core itself * maybe a second cluster
normally on Intel systems, the memory power delta is quite significant which then means the efficiency of the second core is huge compared to running things in sequence.
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