Messages in this thread | | | Date | Mon, 5 Apr 2010 09:40:23 -0700 | From | "Paul E. McKenney" <> | Subject | Re: A few questions and issues with dynticks, NOHZ and powertop |
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On Mon, Apr 05, 2010 at 09:23:16AM -0700, Arjan van de Ven wrote: > On 4/5/2010 9:22, Paul E. McKenney wrote: > >On Mon, Apr 05, 2010 at 09:07:33AM -0700, Arjan van de Ven wrote: > >>On 4/5/2010 8:14, Paul E. McKenney wrote: > >>>So the main issue is that for many workloads, it is best to run full bore > >>>and get done quickly, thus allowing the entire machine to be powered down? > >> > >>yep > >> > >>>If so, it seems likely that there would be some workloads that were sometimes > >>>unable to use all the CPUs, in which case shutting down (idling, offlining, > >>>dyntick-idling, whatever) the excess CPUs might nevertheless be the right > >>>thing to do. > >> > >>but the point is that the normal scheduler + idle behavior gives you exactly that > >>in a natural way ! > >>If you don't have enough work (tasks) to keep all cores busy, the others are and stay idle. > > > >So your earlier objection was not to dyntick-idle as such, but rather > >to artificially constraining the scheduler to induce dyntick-idle? > > my objection was against the notion that offlining cpus helps power/energy ;-)
Fair enough, at least in general. I should hasten to add that Lai's patch also helps in the case where NR_CPUS is greater than the number of CPUs on the system.
Thanx, Paul
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