On Thu, Jan 30, 2020 at 12:43:34AM +0000, Mel Gorman wrote: > On Wed, Jan 29, 2020 at 06:38:52PM +0100, Peter Zijlstra wrote: > > I suppose the fact that it limits it to tasks that were running on the > > same CPU limits the impact if we do get it wrong. > > > > And it's limited to no other task currently running on the > CPU. Now, potentially multiple sleepers are on that CPU waiting for > a mutex/rwsem/completion but it's very unlikely and mostly likely due > to the machine being saturated in which case searching for an idle CPU > will probably fail. It would also be bound by a small window after the > first wakeup before the task becomes runnable before the nr_running check > mitigages the problem. Besides, if the sleeping task is waiting on the > lock, it *is* related to the kworker which is probably finished. > > In other words, even this patches worst-case behaviour does not seem > that bad. OK; let's just stick it in and see what, if anything, falls over :-) I saw there is a v2 out (although I didn't see what changed in a hurry), let me queue that one.
