On 2012-03-28 17:43, Michael S. Tsirkin wrote: > On Wed, Mar 28, 2012 at 01:36:15PM +0200, Jan Kiszka wrote: >> On 2012-03-28 13:31, Michael S. Tsirkin wrote: >>>>>>> Also, how would this support irqfd in the future? Will we have to >>>>>>> rip it all out and replace with per-device tracking that we >>>>>>> have today? >>>>>> >>>>>> Irqfd and kvm device assignment will require additional interfaces (of >>>>>> the kvm core in QEMU) via which you will be able to request stable >>>>>> routes from such sources to specified MSIs. That will be widely >>>>>> orthogonal to what is done in these patches here. >>>>> >>>>> Yes but not exactly as they will conflict for resources, right? >>>>> How do you plan to solve this? >>>> >>>> As done in my original series: If a static route requires a pseudo GSI >>>> and there are none free, we simply flush the dynamic MSI routes. >>> >>> Right. So static routes take precedence. This means that in effect >>> we will have two APIs in qemu: for fast MSIs and for slow ones, >>> the advantage of the slow APIs being that they are easier to use, >>> right? >> >> We will have two APIs depending on the source of the MSI. Special >> sources are the exception while emulated ones are the majority. And for >> the latter we should try very hard to keep things simple and clean. >> >> Jan > > I assume this means yes :) So how about we replace the hash table with a > single GSI reserved for this purpose, and use that for each interrupt? > This will work fine for slow paths such as hotplug controller, yes it > will be slow but *predictably* slow.
AHCI, HDA, virtio-block, and every other userspace MSI user will suffer - I can't imagine you really want this. :) > > Fast path will use static GSIs like qemu-kvm does. Nope, qemu-kvm hooks deeply into the MSI layer to track vectors. I don't believe we want this upstream. It also doesn't work for non-PCI MSI (HPET on x86, try -global hpet.timers=4 -global hpet.msi=on with Linux guests). Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
