On Wed, Jul 09, 2014 at 03:05:56PM +0100, Andrew Cooper wrote: > On 09/07/14 14:59, Konrad Rzeszutek Wilk wrote: > > > >>> +What: /sys/bus/pci/drivers/pciback/irq_handler_state > >>> +Date: Oct 2011 > >>> +KernelVersion: 3.1 > >>> +Contact: xen-de...@lists.xenproject.org > >>> +Description: > >>> + An option to toggle Xen PCI back to acknowledge (or stop) > >>> + interrupts for the specific device regardless of whether > >>> the > >>> + device is shared, enabled, or on a level interrupt line. > >>> + Writing a string of DDDD:BB:DD.F will toggle the state. > >>> + This is Domain:Bus:Device.Function where domain is > >>> optional. > >> I do not understand under what circumstances this should be used in. > > So that dom0 does not disable the IRQ line as it would be getting the IRQs > > for the guest as well (because the IRQ line is level and another guest > > uses an PCI device that is using the same line). > > Why is this relevant? Xen (and Xen alone) actually controls this aspect > of interrupts. Xen manages passing line level interrupts to any domain > which might have a device hanging off a particular line, and has to wait > until all domains have EOI'd the line until it can clear the interrupt > at the IO-APIC.
Because Linux will think there is an IRQ storm as the event->IRQ points to the default one. And then it will mask the event, which means dom0 will mask the PIRQ, and Xen will then also mask the IRQ. > > ~Andrew -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
