On Tue, Apr 4, 2017 at 11:12 PM, Mike Galbraith <efa...@gmx.de> wrote: > On Tue, 2017-04-04 at 22:25 -0700, Cong Wang wrote: >> On Tue, Apr 4, 2017 at 8:20 PM, Mike Galbraith <efa...@gmx.de> wrote: >> > - while (some_qdisc_is_busy(dev)) >> > - yield(); >> > + swait_event_timeout(swait, >> > !some_qdisc_is_busy(dev), 1); >> > } >> >> I don't see why this is an improvement even if I don't care about the >> hardcoded timeout for now... Why the scheduler can make a better >> decision with swait_event_timeout() than with cond_resched()? > > Because sleeping gets you out of the way? There is no other decision > the scheduler can make while a SCHED_FIFO task is trying to yield when > it is the one and only task at it's priority. The scheduler is doing > exactly what it is supposed to do, problem is people calling yield() > tend to think it does something it does not do, which is why it is > decorated with "if you think you want yield(), think again" > > Yes, yield semantics suck rocks, basically don't exist. Hop in your > time machine and slap whoever you find claiming responsibility :)
I am not trying to defend for yield(), I am trying to understand when cond_resched() is not a right solution to replace yield() and when it is. For me, the dev_deactivate_many() case is, because I interpret "be nice" differently. Thanks.
