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. -Mike -- 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/
