On 06/07/10 09:26, Avi Kivity wrote: > The original motivation for moving the PIC and IOAPIC into the kernel > was performance, especially for assigned devices. Both devices are high > interaction since they deal with interrupts; practically after every > interrupt there is either a PIC ioport write, or an APIC bus message, > both signalling an EOI operation. Moving the PIT into the kernel > allowed us to catch up with missed timer interrupt injections, and > speeded up guests which read the PIT counters (e.g. tickless guests). > > However, modern guests running on modern qemu use MSI extensively; both > virtio and assigned devices now have MSI support; and the planned VFIO > only supports kernel delivery via MSI anyway; line based interrupts will > need to be mediated by userspace. The "modern" guest comment is a bit concerning. 2.4 kernels (e.g., RHEL3) use the PIT for timekeeping and will still be around for a while. RHEL4 and RHEL5 will be around for a long time to come. Not sure how those fit within the "modern" label, though I see my RHEL4 guest is using the pit as a timesource. David -- 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
