On Wed, Jul 09, 2014 at 03:22:30PM +0100, Andrew Cooper wrote: > On 09/07/14 15:13, Konrad Rzeszutek Wilk wrote: > > 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. > > Xen will (and by this I mean 'should', and this was the behaviour last > time I delved in there) only mask the IRQ if dom0 is the only consumer > of these interrupts. > > For any PCIPassthrough, dom0 will get line interrupts for passed-through > devices, but in this case pci-back should always handle the line > interrupts so Linux doesn't block them as an IRQ storm.
And that is what it does - and this option provides the option to enable/disable it the system admin wishes to do it. > > ~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/
