On Sun, Sep 21, 2014 at 11:36:44AM +0200, Stefan Fritsch wrote: > On Sunday 21 September 2014 11:09:14, Michael S. Tsirkin wrote: > > On Thu, Sep 18, 2014 at 09:18:37PM +0200, Stefan Fritsch wrote: > > > On Monday 01 September 2014 09:37:30, Michael S. Tsirkin wrote: > > > > Why do we need INT#x? > > > > How about setting IRQF_SHARED for the config interrupt > > > > while using MSI-X? You'd have to read ISR to check that the > > > > interrupt was intended for your device. > > > > > > > > > > > > The virtio 0.9.5 spec says that ISR is "unused" when in MSI-X > > > mode. I don't think that you can depend on the device to set the > > > configuration changed bit. > > > The virtio 1.0 spec seems to have fixed that. > > > > Yes, virtio 0.9.5 has this bug. But in practice qemu always set this > > bit, so for qemu we could do that unconditionally. Pekka's lkvm > > tool doesn't unfortunately. It's easy to fix that, but it would be > > nicer to additionally probe for old versions of the tool, and > > disable IRQF_SHARED in that case. > > What about other implementations? I think Linux should try to conform > to the spec so that all device implementations which conform to the > spec just work. > > One implementation that comes to mind is virtualbox. But from a quick > look at the source, it seems that it sets the ISR bit always, too. And > it uses qemu's subsystem vendor id. > > But there are other implementations. For example bhyve. I couldn't find any code in bhyve that sets VTCFG_ISR_CONF_CHANGED. Maybe it doesn't generate config changed interrupts? bhyve sets subsystem vendor to 0 apparently? We could use that to detect it. But maybe we should just make it a 1.0 only feature. > > > AFAIK a subsystem vendor id does not cost money to register, but > > only pci sig members can do this, and membership costs $3000. > > Maybe we should combine all this with checking subsystem vendor id, > > and only implement the optimization if it matches qemu, for now. > > This needs some thought. > > Maybe the virtio spec should include a way to query the vendor that > does not involve the pci sig. Maybe use a string? Then no registry > would be necessary. We can make the requirement for the vendor specific ID stronger in 1.0, SHOULD instead of MAY. But it seems that people will still copy-paste working code across hypervisors, I'm not sure this can be helped. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
