On Tuesday, February 6, 2018 12:26 AM, Stefan Hajnoczi wrote: > On Fri, Feb 02, 2018 at 09:08:44PM +0800, Wei Wang wrote: > > On 02/02/2018 01:08 AM, Michael S. Tsirkin wrote: > > > On Tue, Jan 30, 2018 at 08:09:19PM +0800, Wei Wang wrote: > > > > Issues: > > > > Suppose we have both the vhost and virtio-net set up, and vhost > > > > pmd <-> virtio-net pmd communication works well. Now, vhost pmd > > > > exits (virtio-net pmd is still there). Some time later, we re-run > > > > vhost pmd, the vhost pmd doesn't know the virtqueue addresses of > > > > the virtio-net pmd, unless the virtio-net pmd reloads to start the > > > > 2nd phase of the vhost-user protocol. So the second run of the vhost > pmd won't work. > > > > > > > > Any thoughts? > > > > > > > > Best, > > > > Wei > > > So vhost in qemu must resend all configuration on reconnect. > > > Does this address the issues? > > > > > > > Yes, but the issues are > > 1) there is no reconnecting when a pmd exits (the socket connection > > seems still on at the device layer); > > This is how real hardware works too. If the driver suddenly stops running > then the device remains operational. When the driver is started again it > resets the device and initializes it. > > > 2) If we find a way to break the QEMU layer socket connection when pmd > > exits and get it reconnect, virtio-net device still won't send all the > > configure when reconnecting, because socket connecting only triggers > > phase 1 of vhost-user negotiation (i.e. vhost_user_init). Phase 2 is > > triggered after the driver loads (i.e. vhost_net_start). If the > > virtio-net pmd doesn't reload, there are no phase 2 messages (like > > virtqueue addresses which are allocated by the pmd). I think we need > > to think more about this before moving forward. > > Marc-André: How does vhost-user reconnect work when the master goes > away and a new master comes online? Wei found that the QEMU slave > implementation only does partial vhost-user initialization upon reconnect, so > the new master doesn't get the virtqueue address and related information. > Is this a QEMU bug?
Actually we are discussing the slave (vhost is the slave, right?) going away. When a slave exits and some moment later a new slave runs, the master (virtio-net) won't send the virtqueue addresses to the new vhost slave. Best, Wei
