On 10/01/2015 04:39 PM, Stephen Hemminger wrote: > On Thu, 1 Oct 2015 16:03:06 -0700 > Alexander Duyck <alexander.duyck at gmail.com> wrote: > >> On 10/01/2015 03:00 PM, Stephen Hemminger wrote: >>> On Thu, 1 Oct 2015 12:48:36 -0700 >>> Alexander Duyck <alexander.duyck at gmail.com> wrote: >>> >>>> On 10/01/2015 07:57 AM, Stephen Hemminger wrote: >>>>> On Thu, 1 Oct 2015 13:59:02 +0300 >>>>> Avi Kivity <avi at scylladb.com> wrote: >>>>> >>>>>> On 10/01/2015 01:28 AM, Stephen Hemminger wrote: >>>>>>> This is a new UIO device driver to allow supporting MSI-X and MSI >>>>>>> devices >>>>>>> in userspace. It has been used in environments like VMware and older >>>>>>> versions >>>>>>> of QEMU/KVM where no IOMMU support is available. >>>>>> Why not add msi/msix support to uio_pci_generic? >>>>> That is possible but that would meet ABI and other resistance from the >>>>> author. >>>>> Also, uio_pci_generic makes it harder to find resources since it doesn't >>>>> fully >>>>> utilize UIO infrastructure. >>>> I'd say you are better off actually taking this in the other direction. >>>> From what I have seen it seems like this driver is meant to deal with >>>> mapping VFs contained inside of guests. If you are going to fork off >>>> and create a UIO driver for mapping VFs why not just make it specialize >>>> in that. You could probably simplify the code by dropping support for >>>> legacy interrupts and IO regions since all that is already covered by >>>> uio_pci_generic anyway if I am not mistaken. >>>> >>>> You could then look at naming it something like uio_vf since the uio_msi >>>> is a bit of a misnomer since it is MSI-X it supports, not MSI interrupts. >>> The support needs to cover: >>> - VF in guest >>> - VNIC in guest (vmxnet3) >>> it isn't just about VF's >> I get that, but the driver you are talking about adding is duplicating >> much of what is already there in uio_pci_generic. If nothing else it >> might be worth while to look at replacing the legacy interrupt with >> MSI. Maybe look at naming it something like uio_pcie to indicate that >> we are focusing on assigning PCIe and virtual devices that support MSI >> and MSI-X and use memory BARs rather than legacy PCI devices that are >> doing things like mapping I/O BARs and using INTx signaling. >> >> My main argument is that we should probably look at dropping support for >> anything that isn't going to be needed. If it is really important we >> can always add it later. I just don't see the value in having code >> around for things we aren't likely to ever use with real devices as we >> are stuck supporting it for the life of the driver. I'll go ahead and >> provide a inline review of your patch 2/2 as I think my feedback might >> make a bit more sense that way. > Ok, but having one driver that can deal with failures with msi-x vector > setup and fallback seemed like a better strategy.
Yes, but in the case of something like a VF it is going to just make a bigger mess of things since INTx doesn't work. So what would you expect your driver to do in that case? Also we have to keep in mind that the MSI-X failure case is very unlikely. One other thing that just occurred to me is that you may want to try using the range allocation call instead of a hard set number of interrupts. Then if you start running short on vectors you don't hard fail and instead just allocate what you can. - Alex
