On Mon, Oct 04, 2010 at 11:20:19AM -0500, Anthony Liguori wrote: > On 10/04/2010 11:12 AM, Michael S. Tsirkin wrote: > >On Mon, Oct 04, 2010 at 09:01:14AM -0500, Anthony Liguori wrote: > >>On 10/04/2010 03:04 AM, Avi Kivity wrote: > >>>On 10/04/2010 03:18 AM, Anthony Liguori wrote: > >>>>On 10/03/2010 09:28 AM, Michael S. Tsirkin wrote: > >>>>>>This is using eventfd as well. > >>>>>Sorry, I meant irqfd. > >>>>I've tried using irqfd in userspace. It hurts performance quite > >>>>a bit compared to doing an ioctl so I would suspect this too. > >>>> > >>>>A last_used_idx or similar mechanism should help performance > >>>>quite a bit on top of ioeventfd too. > >>>> > >>>Any idea why? While irqfd does quite a bit of extra locking, it > >>>shouldn't be that bad. > >>Not really. It was somewhat counter intuitive. > >> > >>A worthwhile experiment might be to do some layering violations and > >>have vhost do an irq injection via an ioctl and see what the > >>performance delta is. > >I think you don't even need to try that hard. > >Just comment this line: > >// proxy->pci_dev.msix_mask_notifier = virtio_pci_mask_notifier; > >this is what switches to irqfd when msi vector is unmasked. > > That drops to userspace though for all irqs, no? Exactly. > Or did you mean that commenting that line out improves performance > demonstrating the overhead of irqfd? > > Regards, > > Anthony Liguori Haven't tried this, but possibly. > >> I suspect it could give vhost a nice boost. > >> > >>Regards, > >> > >>Anthony Liguori -- 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
