On Mon, Jun 04, 2012 at 01:40:28PM +0200, Jan Kiszka wrote: > On 2012-06-04 13:21, Thomas Gleixner wrote: > > On Sun, 3 Jun 2012, Avi Kivity wrote: > > > >> On 06/01/2012 09:26 PM, Jan Kiszka wrote: > >>> > >>>> you suggesting we need a request_edge_threaded_only_irq() API? Thanks, > >>> > >>> I'm just wondering if that restriction for threaded IRQs is really > >>> necessary for all use cases we have. Threaded MSIs do not appear to me > >>> like have to be handled that conservatively, but maybe I'm missing some > >>> detail. > >>> > >> > >> btw, I'm hoping we can unthread assigned MSIs. If the delivery is > >> unicast, we can precalculate everything and all the handler has to do is > >> set the IRR, KVM_REQ_EVENT, and kick the vcpu. All of these can be done > >> from interrupt context with just RCU locking. > > > > There is really no need to run MSI/MSI-X interrupts threaded for > > KVM. I'm running the patch below for quite some time and it works like > > a charm. > > > > Thanks, > > > > tglx > > ---- .... > > This may work in practice but has two conceptual problems: > - we do not want to run a potential broadcast to all VCPUs to run in > a host IRQ handler I'm not sure why this one is a problem: injecting an interrupt once you know the vcpu seems really cheap. It's true that scanning vcpus might take a bit more time when there are lots of them but it's a single linear scan that we do anyway. And we also inject msi from irqfd callback with interrupts disabled which seems equivalent. Pls correct me if I'm wrong. > - crazy user space could have configured the route to end up in the > PIC or IOAPIC, and both are not hard-IRQ safe (this should probably > be caught on setup) Yes this needs to be fixed up. > So this shortcut requires some checks before being applied to a specific > MSI/MSI-X vector. > > > Taking KVM aside, my general question remains if threaded MSI handlers > of all devices really need to apply IRQF_ONESHOT though they should have > no use for it. > > Jan > > -- > Siemens AG, Corporate Technology, CT T DE IT 1 > Corporate Competence Center Embedded Linux > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- 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
