On Sun, Aug 03, 2014 at 09:08:06AM -0600, Alex Williamson wrote: >On Mon, 2014-08-04 at 00:30 +1000, Gavin Shan wrote: >> On Sun, Aug 03, 2014 at 08:57:39AM +0000, Eli Cohen wrote: >> >>> >> >>>What is the problem with masking the interrupts with the PCI command >> >>>register? I'm asking because I want to understand in which devices we >> >>>have the problem, and if it could be fixed by firmware guys. >> >>>What are the implications of having the quirk? >> >>> >> > >> >>The way to mask the interrupt through PCI command register isn't taking effect on IBM power platform. So we have to have the >quirk so that the interrupt could be masked from interrupt controller side with function disable_irq_nosync(). >> >> >> >>If the interrupt can't be masked properly, we detect interrupt storm reported from host/guest when passing through those devices >via VFIO without suprise. >> > >> >Hi Gavin, >> >Does it have any effect on performance. Also, can you tell in which cases interrupts need to be masked? >> > >> >> Eli, more code needed to be run for masking the LSI from interrupt controller >> side than from PCI command register. >> >> I was passing through Mellanox devices from host to guest with VFIO, and I >> designated to use LSI in the guest side. More details could be found in >> drivers/vfio/pci/vfio_pci_intrs.c::vfio_intx_handler() > >INTx is relatively high overhead already for device assignment since the >interrupt is level triggered and needs to be masked on the host while >the guest is processing it. The more important restriction imposed by >marking broken INTx masking is that the device needs an exclusive >interrupt line in order to be assigned to a guest. That may be common >practice on IBM power, but on x86 it can make it much harder to >configure the system for this use case. Thanks, > Power platform has the similar situation: Each PCI controller has 4 LSIs shared by all child devices attached to the PHB. It would be racy if one LSI is shared by 2 or more devices. So masking LSI with PCI command register is the preferred mechanism. Unfortunately, it doesn't work on those 2 Mellanox devices. With the quirk, it's workable at least. Thanks, Gavin >Alex > > -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
