On Mon, Jul 27, 2009 at 11:21:39AM +0300, Michael S. Tsirkin wrote: > On Mon, Jul 27, 2009 at 11:13:50AM +0300, Gleb Natapov wrote: > > On Mon, Jul 27, 2009 at 11:02:06AM +0300, Michael S. Tsirkin wrote: > > > On Mon, Jul 27, 2009 at 10:31:38AM +0300, Gleb Natapov wrote: > > > > On Mon, Jul 27, 2009 at 09:28:34AM +0300, Michael S. Tsirkin wrote: > > > > > On Mon, Jul 27, 2009 at 08:33:12AM +0300, Gleb Natapov wrote: > > > > > > On Sun, Jul 26, 2009 at 07:22:25PM +0300, Michael S. Tsirkin wrote: > > > > > > > Here's an untested patch with partial support for level triggered > > > > > > > interrupts in irqfd. What this patch has: support for clearing interrupt > > > > > > > on ack. What this patch does not have: support signalling eventfd on ack > > > > > > > so that userspace can take action and e.g. reenable interrupt. > > > > > > > > > > > > > Do we want level triggered irqfd to be used only for device assignment? > > > > > > > > > > generally level triggered-not only. > > > > > But irqfd is promarily for device assignment and emulated devices. > > > > > > > > > If it is for emulated device zeroing irq level on ack is not acceptable. > > > > > > OK, forget about emulated devices for now. Let's focus on assigned > > > devices. > > > > > Can't. We should design interface that works for everything. > > We can always add the KVM_MAKE_COFFEE ioctl later. > Assigned devices are non interesting case, so we can hack something afterwards to make it work. Emulated devices is a normal case that should work when interface is introduced. Why assigning devices through the kernel is not good enough? What is the reason to push it to userspace? > > > > > > Because if not it is not appropriate to zero irq level on ack. > > > > > > > > > > The bit that is missing in this patch, is that we'll signal eventfd > > > > > after we zero irq. Userspace polls that and re-asserts irq. > > > > That is not needed for device emulation. Emulated device should lower > > > > irq line by itself. It know exactly when to do it. Please don't push > > > > broken device assignment model to emulated devices. > > > > > > > > > > > > > > > And you > > > > > > have no other way to zero irq level?! > > > > > > > > > > The reason is interrupt sharing: device can assert interrupt > > > > > but can not clear it by itself. > > > > For interrupt sharing to work you need to allocate source id for each > > > > irqfd. > > > > > > BTW, current SET_IRQ_LINE interface uses a common source id for all > > > irqs. Does this mean that interrupt sharing in guest is broken now? > > No. It means that sharing in handled in userspace by chipset emulation. > > Aha. Where's that code in qemu-kvm? I only see it forwarding to the AFAIR in hw/pci.c and/or hw/piix_pci.c. > ioctl call directly. And what about assigned devices? These bypass qemu. > Each assigned device allocates its own source id. This is the reason source id exists at all. -- 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
