On Thu, Jul 19, 2012 at 10:11:49AM +0100, Stefan Hajnoczi wrote: > On Wed, Jul 18, 2012 at 4:40 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Wed, Jul 18, 2012 at 04:07:45PM +0100, Stefan Hajnoczi wrote: > >> Optimize for the MSI-X enabled and vector unmasked case where it is > >> possible to issue the KVM ioctl() directly instead of using irqfd. > > > > Why? Is an ioctl faster? > > I have no benchmark results comparing irqfd against direct ioctl. It > would be interesting to know if this "optimization" is worthwhile and > how much of a win it is. > > The reasoning is that the irqfd code path signals an eventfd and then > kvm.ko's poll handler injects the interrupt. The ioctl calls straight > into kvm.ko and skips the signalling/poll step. > > Stefan Polling is done in kernel so at least for MSI it's just a function call. In fact ATM irqfd is more optimized. Maybe it's faster for level IRQs but do we really care? -- MST -- 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
