On Wed, Oct 10, 2012 at 01:31:52PM -0600, Alex Williamson wrote: > On Tue, 2012-10-09 at 09:09 +0200, Jan Kiszka wrote: > > On 2012-10-08 23:11, Alex Williamson wrote: > > > On Mon, 2012-10-08 at 23:40 +0200, Michael S. Tsirkin wrote: > > >> On Mon, Oct 08, 2012 at 01:27:33PM -0600, Alex Williamson wrote: > > >>> On Mon, 2012-10-08 at 22:15 +0200, Michael S. Tsirkin wrote: > > >>>> On Mon, Oct 08, 2012 at 09:58:32AM -0600, Alex Williamson wrote: > > >>>>> Michael, Jan, > > >>>>> > > >>>>> Any comments on these? I'd like to make the PCI changes before I > > >>>>> update > > >>>>> vfio-pci to make use of the new resampling irqfd in kvm. We don't > > >>>>> have > > >>>>> anyone officially listed as maintainer of pci-assign since it's been > > >>>>> moved to qemu. I could include the pci-assign patches in my tree if > > >>>>> you > > >>>>> prefer. Thanks, > > >>>>> > > >>>>> Alex > > >>>> > > >>>> Patches themselves look fine, but I'd like to > > >>>> better understand why do we want the INTx fallback. > > >>>> Isn't it easier to add intx routing support? > > >>> > > >>> vfio-pci can work with or without intx routing support. Its presence is > > >>> just one requirement to enable kvm accelerated intx support. Regardless > > >>> of whether it's easy or hard to implement intx routing in a given > > >>> chipset, I currently can't probe for it and make useful decisions about > > >>> whether or not to enable kvm support without potentially hitting an > > >>> assert. It's arguable how important intx acceleration is for specific > > >>> applications, so while I'd like all chipsets to implement it, I don't > > >>> know that it should be a gating factor to chipset integration. Thanks, > > >>> > > >>> Alex > > >> > > >> Yes but there's nothing kvm specific in the routing API, > > >> and IIRC it actually works fine without kvm. > > > > > > Correct, but intx routing isn't very useful without kvm. > > > > Right now: yes. Long-term: no. The concept in general is also required > > for decoupling I/O paths lock-wise from our main thread. We need to > > explore the IRQ path and cache it in order to avoid taking lots of locks > > on each delivery, possibly even the BQL. But we will likely need > > something smarter at that point, i.e. something PCI-independent. > > That sounds great long term, but in the interim I think this trivial > extension to the API is more than justified. I hope that it can go in > soon so we can get vfio-pci kvm intx acceleration in before freeze > deadlines get much closer. Thanks, > > Alex
Simply reorder the patches: 1. add vfio acceleration with no fallback 2. add way for intx routing to fail 3. add vfio fallback if intx routing fails Then we can apply 1 and argue about the need for 2/3 afterwards. -- MST
