On 05/09/2014 03:34 AM, Mike Galbraith wrote: > On Fri, 2014-05-09 at 01:27 -0400, Rik van Riel wrote: >> On Thu, 08 May 2014 22:20:25 -0400 >> Rik van Riel <r...@redhat.com> wrote: >> >>> Looks like SD_BALANCE_WAKE is not gotten from the sd flags at >>> all, but passed into select_task_rq by try_to_wake_up, as a >>> hard coded sd_flags argument. >> >>> Should we do that, if SD_WAKE_BALANCE is not set for any sched domain? >> >> I answered my own question. The sd_flag SD_WAKE_BALANCE simply means >> "this is a wakeup of a previously existing task, please place it >> properly". >> >> However, it appears that the current code will fall back to the large >> loop with select_idlest_group and friends, if prev_cpu and cpu are not >> part of the same SD_WAKE_AFFINE sched domain. That is a bug... > > ttwu(): cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags); > > We pass SD_BALANCE_WAKE for a normal wakeup, so sd will only be set if > we encounter a domain during traversal where Joe User has told us to do > (expensive) wake balancing before we hit a domain shared by waker/wakee. > > The user can turn SD_WAKE_AFFINE off beyond socket, and we'll not pull > cross node on wakeup. > > Or, you could create an override button to say despite SD_WAKE_AFFINE > perhaps having been set during domain construction (because of some > pseudo-random numbers), don't do that if we have a preferred node, or > just make that automatically part of having numa scheduling enabled, and > don't bother wasting cycles if preferred && this != preferred.
That's not the problem. The problem is that if we do not do an affine wakeup, due to SD_WAKE_AFFINE not being set on a top level domain, we will not try to run p on prev_cpu, but we will fall through into the loop with find_idlest_group, etc... -- All rights reversed -- 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/
