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. 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. > 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. Thanks. -- tejun -- 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/