On Thu, Jun 21, 2018 at 06:07:18PM -0700, Siwei Liu wrote: > On Thu, Jun 21, 2018 at 11:14 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Wed, Jun 13, 2018 at 01:40:59PM +0800, Jason Wang wrote: > >> > >> > >> On 2018年06月13日 12:24, Samudrala, Sridhar wrote: > >> > On 6/12/2018 7:38 PM, Jason Wang wrote: > >> > > > >> > > > >> > > On 2018年06月12日 19:54, Michael S. Tsirkin wrote: > >> > > > On Wed, Jun 06, 2018 at 10:29:03AM +0800, Jason Wang wrote: > >> > > > > > >> > > > > On 2018年06月05日 20:33, Michael S. Tsirkin wrote: > >> > > > > > I don't think this is sufficient. > >> > > > > > > >> > > > > > If both primary and standby devices are present, a > >> > > > > > legacy guest without > >> > > > > > support for the feature might see two devices with same mac and get > >> > > > > > confused. > >> > > > > > > >> > > > > > I think that we should only make primary visible after > >> > > > > > guest acked the > >> > > > > > backup feature bit. > >> > > > > I think we want exactly the reverse? E.g fail the > >> > > > > negotiation when guest > >> > > > > does not ack backup feature. > >> > > > > > >> > > > > Otherwise legacy guest won't even have the chance to see > >> > > > > primary device in > >> > > > > the guest. > >> > > > That's by design. > >> > > > >> > > So management needs to know the capability of guest to set the > >> > > backup feature. This looks a chicken or egg problem to me. > >> > > >> > I don't think so. If the tenant requests 'accelerated datapath feature', > >> > the management > >> > will set 'standby' feature bit on virtio-net interface and if the guest > >> > virtio-net driver > >> > supports this feature, then the tenant VM will get that capability via a > >> > hot-plugged > >> > primary device. > >> > >> Ok, I thought exactly the reverse because of the commit title is "enable > >> virtio_net to act as a standby for a passthru device". But re-read the > >> commit log content, I understand the case a little bit. Btw, VF is not > >> necessarily faster than virtio-net, especially consider virtio-net may have > >> a lot of queues. > > > > Don't do that then, right? > > I don't understand. Where did the standby feature come to imply the > "accelerated datapath" thing? > Isn't failover/standby a generic high > availblity term, rather than marry it to the concept of device model > specifics? Do we expect scsi to work exactly the same way with > "accelerated datapath"? That's not what I said. The semantics are that the primary is always used if present in preference to standby. Jason said virtio net is sometimes preferable. If that's the case don't make it a standby. More advanced use-cases do exist and e.g. Alexander Duyck suggested using a switch-dev. failover isn't it though. -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
