On Wed, Aug 26, 2009 at 10:38:42AM -0300, Marcelo Tosatti wrote: > > > > > If you don't have a host timer emulating the guest PIT, to periodically > > > > > bang on kvm_set_irq, how do you know when to attempt reinjection? > > > > > > > > > > You keep calling kvm_set_irq on every guest entry to figure out when > > > > > reinjection is possible? > > > > If we have timer to inject then yes. It is relatively cheap. Most of the > > > > time pending count will be zero. > > > > > > Won't work with non-tick-based emulation on the host. > > Why? This is the most important point, can you elaborate? > > >From http://www.mail-archive.com/kvm@xxxxxxxxxxxxxxx/msg18644.html. > > An injectable timer interrupt is defined by: > > - time(now) >= time(next_expiration) > - Previous timer interrupt has been acked (thus we can inject). > > The thing is, sure you can drop ack notifiers and check IRR > on every guest entry, but why bother if you can receive an > asynchronous notification? > > Would you prefer to replace > > + if (!ktimer->can_inject) > > With > kvm_set_irq() > > ? > > Not relatively cheap. Most of the times time(now) will be less then time(next_expiration) so on most entries kvm_set_irq() will not be called at all. When interrupt has to be injected I prefer to try to inject it ASAP. PIC and APIC effectively have 2 element interrupt queue (irr/isr) so injection may succeed even though ack was not yet received. -- 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
