[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 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 original commit isn't very enlightening either. David _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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