On 1 June 2016 at 02:01, Yuyang Du <yuyang...@intel.com> wrote: > On Wed, Jun 01, 2016 at 07:07:13AM +0200, Mike Galbraith wrote: >> On Tue, 2016-05-31 at 09:31 +0800, Yuyang Du wrote: >> > On Tue, May 31, 2016 at 11:21:46AM +0200, Peter Zijlstra wrote: >> > > On Tue, May 31, 2016 at 09:11:37AM +0800, Yuyang Du wrote: >> > > > The SD_BALANCE_WAKE is irrelevant in the contexts of these two >> > > > removals, >> > > > and in addition SD_BALANCE_WAKE is not and should not be set in any >> > > > sched_domain flags so far. >> > > >> > > This Changelog doesn't make any sense... >> > >> > How? SD_BALANCE_WAKE is not in any sched_domain flags (sd->flags), even if >> > it is, it is not used anywhere, no? >> >> If the user chooses to set SD_BALANCE_WAKE in sd->flags, it is in fact >> used. It's just not turned on by default due to full balance on every >> wakeup being far too painful to do by default. > > Yup. Up to this point, we don't have any disagreement. And I don't think we > have any disagreement conceptually. What the next patch really does is: > > (1) we don't remove SD_BALANCE_WAKE as an important sched_domain flag, on > the contrary, we strengthen it. > > (2) the semantic of SD_BALANCE_WAKE is currently represented by > SD_WAKE_AFFINE, > we actually remove this representation. > > (3) regarding the semantic of SD_WAKE_AFFINE, it is really not about selecting > waker CPU or about the fast path. Conceptually, it is just saying the > waker > CPU is a valid and important candidate if SD_BALANCE_WAKE, which is just > so > obvious, so I don't think it deserves to be a separate sched_domain flag. > > (4) the outcome is, if SD_BALANCE_WAKE, we definitely will/should try waker > CPU, > and if !SD_BALANCE_WAKE, we don't try waker CPU. So nothing functional is > changed.
AFAIU, there is 4 possible cases during wake up: - we don't want any balance at wake so we don't have SD_BALANCE_WAKE nor SD_WAKE_AFFINE in sched_domain->flags - we only want wake affine balance check so we only have SD_WAKE_AFFINE in sched_domain->flags - we want wake_affine and full load balance at wake so we have both SD_BALANCE_WAKE and SD_WAKE_AFFINE in sched_domain->flags - we want full load balance but want to skip wake affine fast path so we only have SD_BALANCE_WAKE in sched_domain->flags I'm not sure that we can still do only wake_affine or only full load_balance with your changes whereas these sequences are valid ones Vincent
