If my understanding is correct, on a resume operation, we have the following callback trace: 1. virtio_pci_restore function that calls all restore call back of virtio devices 2. virtnet_restore that calls try_fill_recv function for each virtual queues 3. try_fill_recv function kicks the virtual queue (through virtqueue_kick function)
On Tue, Jun 16, 2015 at 7:29 AM, Jason Wang <jasow...@redhat.com> wrote: > > > 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. >
