On Tue, Jun 17, 2014 at 6:25 PM, Cornelia Huck <cornelia.h...@de.ibm.com> wrote: > On Tue, 17 Jun 2014 18:15:39 +0800 > Ming Lei <ming....@canonical.com> wrote: > >> On Tue, Jun 17, 2014 at 4:46 PM, Cornelia Huck <cornelia.h...@de.ibm.com> >> wrote: >> >> >> >> Looks like s390 virtio-blk never enables the two common features, is >> >> there any reason the two features can't be supported by s390? >> > >> > Indirect descriptors are fine. event_idx will not work IIUC because we >> > always need to do a sync before we see changes, and this needs an >> > interrupt to trigger. >> >> Sounds like the old s390 isn't cache coherent? Because you mean >> write in one side can only be observed from another side with an >> explicit notification or interrupt. >> >> On arm/arm64, we didn't see any problem with event_idx. > > But you probably have the queues in guest memory, as on other > transports (including virtio-ccw)? The old s390-virtio transport keeps > the devices and their virtqueues in a memory area behind the guest > memory - the guest does not see that memory directly, but a sync has to > be performed to see virtqueue movement (see s390_virtio_device_sync()).
OK, it looks like a real physical device, :-) I will keep s390-virtio as it is, thanks for your explanation. Thanks, -- Ming Lei
