On 06/16/2015 03:24 PM, Thibaut Collet wrote: > 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)
Yes, but this happens only after pm resume not migration. Migration is totally transparent to guest. > > > 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.
