On Wed, Oct 21, 2009 at 11:34:51AM -0400, Gregory Haskins wrote: > Gleb Natapov wrote: > > On Wed, Oct 21, 2009 at 10:34:53AM -0400, Gregory Haskins wrote: > >> IRQFD currently uses a deferred workqueue item to execute the injection > >> operation. It was originally designed this way because kvm_set_irq() > >> required the caller to hold the irq_lock mutex, and the eventfd callback > >> is invoked from within a non-preemptible critical section. > >> > >> With the advent of lockless injection support in kvm_set_irq, the deferment > >> mechanism is no longer technically needed. Since context switching to the > >> workqueue is a source of interrupt latency, lets switch to a direct > >> method. > >> > > kvm_set_irq is fully lockless only in MSI case. IOAPIC/PIC has mutexes. > > Right, but irqfd by design only works with MSI (or MSI like edge > triggers) anyway. Legacy-type injections follow a different path. > Ah, If this the case and it will stay that way then the change looks OK to me. > In any case, I didn't change the locking (you did ;). You recently > patched the irqfd code to remove the irq_lock, but we still had the > deferment mechanism in place to avoid the mutex_lock from within the > POLLIN callback. Since the mutex_lock is now no longer acquired in this > path, the deferment technique is not needed either. Its only adding > overhead for no purpose. So I am simply cleaning that up to improve > interrupt performance. > > HTH, > -Greg > > -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
