On Thu, Apr 28, 2016 at 03:24:43AM -0700, tip-bot for Peter Zijlstra wrote: > Commit-ID: 2548d546d40c0014efdde88a53bf7896e917dcce > Gitweb: http://git.kernel.org/tip/2548d546d40c0014efdde88a53bf7896e917dcce > Author: Peter Zijlstra <[email protected]> > AuthorDate: Thu, 21 Apr 2016 18:03:15 +0200 > Committer: Ingo Molnar <[email protected]> > CommitDate: Thu, 28 Apr 2016 10:28:55 +0200 > > nohz/full, sched/rt: Fix missed tick-reenabling bug in sched_can_stop_tick() > > Chris Metcalf reported a that sched_can_stop_tick() sometimes fails to > re-enable the tick. > > His observed problem is that rq->cfs.nr_running can be 1 even though > there are multiple runnable CFS tasks. This happens in the cgroup > case, in which case cfs.nr_running is the number of runnable entities > for that level. > > If there is a single runnable cgroup (which can have an arbitrary > number of runnable child entries itself) rq->cfs.nr_running will be 1. > > However, looking at that function I think there's more problems with it. > > It seems to assume that if there's FIFO tasks, those will run. This is > incorrect. The FIFO task can have a lower prio than an RR task, in which > case the RR task will run. > > So the whole fifo_nr_running test seems misplaced, it should go after > the rr_nr_running tests. That is, only if !rr_nr_running, can we use > fifo_nr_running like this.
Thanks for this patch. I indeed made confusions around SCHED_RR and SCHED_FIFO priorities. Too late for me to ACK but I would have. Thanks!
