[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3 1/7] xen-pciback: Document the various parameters and attributes in SysFS
On Wed, Jul 09, 2014 at 03:45:03PM +0100, David Vrabel wrote: > On 09/07/14 15:25, Konrad Rzeszutek Wilk wrote: > > 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-devel@xxxxxxxxxxxxxxxxxxxx > >>>>>>> +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. > > I still don't understand why someone would want to flip the handler to > a broken mode. The intent was to allow you to flip to the 'enable' mode in case Linux did not detect it correctly. > > The original commit isn't very enlightening either. Thoughts then on what this documentation patch should say to make it clear of its intent? > > David _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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