On Tue, May 20, 2014 at 10:35:34AM -0400, Tejun Heo wrote: > Hello, > > On Tue, May 20, 2014 at 04:32:31PM +0200, Frederic Weisbecker wrote: > > > But that's the same for other pwqs too. Back-to-back requeueing will > > > hold back pwq switching on any workqueue. > > > > I don't think so, because non ordered pwqs aren't created with 0 max_active, > > so they can run before the old pwq is released. It's not holding back the > > new > > one and creating a starvation there. > > > > But maybe I forget other details. > > Ah, I was thinking about old pwq not being allowed to be released > while one or more work items are requeueing themselves back-to-back.
Right. OTOH, if you have non-deffered work items requeuing themselves back to back for ever, you may have a much bigger problem than just a few unreleased bytes :) > Yeap, the new ones can still be used for other work items. > > > > Maybe I'm confused but I don't think it'd be. Let's say there was an > > > attribute change with one work item, A, which is performing > > > back-to-back requeueing and another one, B, which queues itself > > > intermittently. If B is queued while A is executing, followed by A > > > requeueing itself, the expected execution order is A - B - A; however, > > > without the above exception for ordered workqueues, it'd end up A - A > > > - B because B will end up on the new pwq while A on the older one and > > > max_active won't be transferred to the new pwq before it becomes > > > empty. > > > > Ah right AAB instead of ABA is possible indeed. I don't know if some > > workqueue > > rely on such guarantee but it's possible. > > That's part of the ordering guarantee of ordered workqueues so we > better not break it. Ok. > > > In which case we have one more reason to make an exception on ordered > > workqueues > > previous pwq reuse. > > Yeah, I agree the special treatment is necessary but the current > comment is misleading. Ok got it, I'll try to improve the comment. Thanks. -- 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/
