On 8/16/12, Peter Zijlstra <pet...@infradead.org> wrote: > On Thu, 2012-08-16 at 19:45 +0600, Rakib Mullick wrote: >> When a CPU is about to go down, it moves all it's sleeping task to an >> active CPU, then nr_uninterruptible counts are >> also moved. When moving nr_uninterruptible count, currently it chooses a >> randomly picked CPU from the active CPU mask >> to keep the global nr_uninterruptible count intact. But, it would be >> precise to move nr_uninterruptible counts to the >> CPU where all the sleeping tasks were moved and it also might have subtle >> impact over rq's load calculation. So, this >> patch is prepared to address this issue. > > The Changelog is ill-formated. Other than that, the patch doesn't appear > to actually do what it says. The sleeping tasks can be scattered to any > number of cpus as decided by select_fallback_rq(). > I'm not sure which parts are missing from Changelog to patch. And this patch assumes that, sleeping tasks won't be scattered. From select_fallback_rq(), sleeping tasks might get scattered due to various cases like. if CPU is down, task isn't allowed to move a particular CPU. Other than that, dest cpu supposed to be the same.
> Furthermore there should be absolutely no impact on load calculation > what so ever. nr_uninterruptible is only ever useful as a sum over all > cpus, this total sum doesn't change regardless of where you put the > value. > > Worse, there's absolutely no relation to the tasks on the runqueue > (sleeping or otherwise) and nr_uninterruptible, so coupling these > actions makes no sense what so ever. > nr_uninterruptible is coupled with tasks on the runqueue to calculate nr_active numbers. In calc_load_fold_active(), this nr_active numbers are used to calculate delta. This is how I understand this part and seeing some impact. Thanks, Rakib -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
