On 06/15/2015 08:12 PM, Thibaut Collet wrote: > 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 ?
I must miss something but migration should be transparent to guest. Could you show me the code that guest does the kick after migration? > > 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.