On 09/26/2013 08:29 AM, Andrew Morton wrote: > On Thu, 26 Sep 2013 03:50:16 +0200 Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: > >> On Wed, Sep 25, 2013 at 06:21:29PM -0700, Andrew Morton wrote: >>> On Wed, 25 Sep 2013 18:15:21 -0700 Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> wrote: >>> >>>> On 9/25/2013 4:47 PM, Andi Kleen wrote: >>>>>> Also, the changelogs don't appear to discuss one obvious downside: the >>>>>> latency incurred in bringing a bank out of one of the low-power states >>>>>> and back into full operation. Please do discuss and quantify that to >>>>>> the best of your knowledge. >>>>> >>>>> On Sandy Bridge the memry wakeup overhead is really small. It's on by default >>>>> in most setups today. >>>> >>>> btw note that those kind of memory power savings are content-preserving, >>>> so likely a whole chunk of these patches is not actually needed on SNB >>>> (or anything else Intel sells or sold) >>> >>> (head spinning a bit). Could you please expand on this rather a lot? >> >> As far as I understand there is a range of aggressiveness. You could >> just group memory a bit better (assuming you can sufficiently predict >> the future or have some interface to let someone tell you about it). >> >> Or you can actually move memory around later to get as low footprint >> as possible. >> >> This patchkit seems to do both, with the later parts being on the >> aggressive side (move things around) >> >> If you had non content preserving memory saving you would >> need to be aggressive as you couldn't afford any mistakes. >> >> If you had very slow wakeup you also couldn't afford mistakes, >> as those could cost a lot of time. >> >> On SandyBridge is not slow and it's preserving, so some mistakes are ok. >> >> But being aggressive (so move things around) may still help you saving >> more power -- i guess only benchmarks can tell. It's a trade off between >> potential gain and potential worse case performance regression. >> It may also depend on the workload. >> >> At least right now the numbers seem to be positive. > > OK. But why are "a whole chunk of these patches not actually needed on SNB > (or anything else Intel sells or sold)"? What's the difference between > Intel products and whatever-it-is-this-patchset-was-designed-for? > Arjan, are you referring to the fact that Intel/SNB systems can exploit memory self-refresh only when the entire system goes idle? Is that why this patchset won't turn out to be that useful on those platforms? Regards, Srivatsa S. Bhat -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>