After a resume operation the guest always kicks the backend for each virtual queues. A live migration does a suspend operation on the old host and a resume operation on the new host. So the backend has a kick after migration.
I have checked this point with a legacy guest (redhat 6-5 with kernel version 2.6.32-431.29.2) and the kick occurs after migration or resume. Jason have you an example of legacy guest that will not kick the virtual queue after a resume ? On Mon, Jun 15, 2015 at 10:44 AM, Michael S. Tsirkin <m...@redhat.com> wrote: > On Mon, Jun 15, 2015 at 03:43:13PM +0800, Jason Wang wrote: >> >> >> On 06/12/2015 10:28 PM, Michael S. Tsirkin wrote: >> > On Fri, Jun 12, 2015 at 03:55:33PM +0800, Jason Wang wrote: >> >> >> >> On 06/11/2015 08:13 PM, Michael S. Tsirkin wrote: >> >>> On Thu, Jun 11, 2015 at 02:10:48PM +0200, Thibaut Collet wrote: >> >>>> I am not sure to understand your remark: >> >>>> >> >>>>> It needs to be sent when backend is activated by guest kick >> >>>>> (in case of virtio 1, it's possible to use DRIVER_OK for this). >> >>>>> This does not happen when VM still runs on source. >> >>>> Could you confirm rarp can be sent by backend when the >> >>>> VHOST_USER_SET_VRING_KICK message is received by the backend ? >> >>> No - the time to send pakets is when you start processing >> >>> the rings. >> >>> >> >>> And the time to do that is when you detect a kick on >> >>> an eventfd, not when said fd is set. >> >>> >> >> Probably not. What if guest is only doing receiving? >> > Clarification: the kick can be on any VQs. >> > In your example, guest kicks after adding receive buffers. >> >> Yes, but refill only happens on we are lacking of receive buffers. It is >> not guaranteed to happen just after migration, we may have still have >> enough rx buffers for device to receive. > > I think we also kick the backend after migration, do we not? > Further, DRIVER_OK can be used as a signal to start backend too. > >> > >> >> In this case, you >> >> won't detect any kick if you don't send the rarp first.
