On Fri, 2013-06-21 at 14:34 -0700, Arjan van de Ven wrote: > 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
Sort-of. We have something similar with threads on ppc. IE, the core can only really stop if all threads are. From a Linux persepctive it's a matter of how we define the scope of that 'cluster' Catalin is talking about. I'm sure you do too. Then there is the package, which adds MC etc... > 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. What's your typical latency for bringing an MC back (and memory out of self refresh) ? IE. Basically bringing a package back up ? Cheers, Ben. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
