On 12/13/17 10:29, Paolo Bonzini wrote: > On 13/12/2017 09:35, Laszlo Ersek wrote: >> I consider the lack of a "VIRTIO_SCSI_F_MQ" feature bit an issue with >> the virtio specification (and consequently with vhost-scsi), not with >> the guest driver(s). > > VIRTIO_SCSI_F_MQ does not exist because virtio-scsi has _always_ > supported multiqueue and has always had a "num_queues" field in the > configuration space. For virtio-net, VIRTIO_NET_F_MQ does not say "the > device or driver knows about multiqueue", it says "the device or driver > wants to read max_virtqueue_pairs" from configuration space. It's > perfectly fine for a device to propose VIRTIO_NET_F_MQ and set > max_virtqueue_pairs=1, or for a driver to negotiate VIRTIO_NET_F_MQ and > then skip initialization of some virtqueues. > > This also means that Maxime's patch to DPDK is also not enough. :) > Virtio-net actually does have a configuration mechanism for multiqueue, > namely the VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET command; the driver sends > that command specifying the number of the transmit and receive queues to > use. However, in my understanding, that command is only needed for the > device to configure receive flow steering, so virtio-scsi doesn't need > that either. > >> Perhaps you can update vhost-scsi similarly to the last patch of >> Maxime's v4 series, even without "VIRTIO_SCSI_F_MQ" -- in the >> SET_FEATURES request handler, just destroy the unused virtqueues that >> have not been configured by the guest driver until that time? > > Yes, this is the right solution. We can assume that if the descriptor > address is equal to zero, the queue is not in use. This is not in the > spec as far as I can see, but it is QEMU's assumption. I will send a > patch to the virtio specification.
Thank you Paolo! Laszlo _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
