On Thu, 2016-01-14 at 22:42 -0800, Frederick N. Brier wrote: > I think I faux pas'd. I just bought a 4-port USB PCI card. I > determined the Ids and updated the /etc/modprobe.d/local.conf as per > the blog tutorial. When I check with "lspci -nnk", the "Kernel > driver in use" shows "uhci_hcd", not "vfio-pci" as the secondary ATI > Video card does. I just saw Alex's post about conventional PCI not > including a requester ID in bus transactions. I must have missed > that in the technology overview. So even though I only have a single > PCI slot on my Asus M5A99FX Pro and it is in its own IOMMU group, it > still is not going to work, correct? I just wanted to double check > whether I need to buy a PCI-E card and wait till Monday to get it, or > if I might just be missing a piece of configuration. The VM's > dedicated USB card is going to provide keyboard and mouse via a 4- > port KVM. I am trying to have a completely isolated USB hub for the > VM. Thank you.
Being conventional PCI doesn't automatically exclude the device from device assignment, it just often comes with complications. The device itself doesn't have a requester ID for the iommu, but the PCIe-to-PCI bridge adds one. The side-effect is that the iommu cannot distinguish between separate devices behind the same bridge, so if you had multiple devices in the iommu group and tried to use the ACS override patch to split them apart, this would fail miserably. You don't have that situation apparently. Another issue can be the PCIe-to-PCI bridge itself, some of these just horrible pieces of hardware, such as the Asmedia bridge on my motherboard. Interrupts don't work right across it, on bare metal or assigned. If you end up with that kind of bad hardware, those conventional PCI slots are really just decoration. Then of course comes the actual endpoint. It's really hard to find conventional PCI cards that support MSI, so you're likely stuck with legacy interrupts. That's not necessarily a problem, but the preferred way to do interrupt masking at the device level is with a feature that was adding in the PCI v2.3 spec. Lots of conventional PCI cards pre- date this spec and lots of others were very broken with this method of interrupt masking. If that method is not available, then we need to mask interrupts at the APIC. This unfortunately requires an exclusive interrupt for the device, which is not always easy or possible to achieve. So, try it and see, but it may be more trouble than it's worth. Even if you only need USB1/2, you may see better overall VM performance with USB3 hardware. The older OHCI/UHCI/EHCI standards seem to use sub-page resources and some of them imply I/O port usage. These incur higher overhead because they cannot be directly mapped into the VM address space. The throughput for the device may be fine, but it'll take more CPU power on the host to do it and may result poor overall performance. Personally I like the TI USB3 cards, more expensive, but not crap. YMMV. Thanks, Alex _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://www.redhat.com/mailman/listinfo/vfio-users
