On Monday 10 June 2013 10:03:00 Alan Stern wrote: > [Thomas and Steve, please see the question below.] > > On Mon, 10 Jun 2013, Ming Lei wrote: > > That isn't clear. It is documented that USB completion handlers are > called with local interrupts disabled. An IRQ arriving before the > tasklet starts up might therefore be serviced during the short interval > before the tasklet disables local interrupts, but if that happens it > would mean that the completion handler would be delayed. That is what tasklets do by definition, isn't it? > In effect, you are prioritizing other IRQs higher than USB completion > handlers. Nevertheless, the total time spent with interrupts disabled > will remain the same. It pobably slightly increases. You have colder caches twice. And potentially you swich CPUs. > (There's one other side effect that perhaps you haven't considered. > When multiple URBs are addressed to the same endpoint, their completion > handlers are called in order of URB completion, which is the same as > the order of URB submission unless an URB is cancelled. By delegating > the completion handlers to tasklets, and particularly by using per-CPU > tasklets, you may violate this behavior.) This is quite serious. It mustn't happen. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
