On Thu, Feb 21, 2019 at 03:33:24AM +0000, Gonglei (Arei) wrote: > > > -----Original Message----- > > From: Zhao Yan [mailto:yan.y.z...@intel.com] > > Sent: Thursday, February 21, 2019 9:59 AM > > To: Gonglei (Arei) <arei.gong...@huawei.com> > > Cc: alex.william...@redhat.com; qemu-devel@nongnu.org; > > intel-gvt-...@lists.freedesktop.org; zhengxiao...@alibaba-inc.com; > > yi.l....@intel.com; eskul...@redhat.com; ziye.y...@intel.com; > > coh...@redhat.com; shuangtai....@alibaba-inc.com; dgilb...@redhat.com; > > zhi.a.w...@intel.com; mlevi...@redhat.com; pa...@linux.ibm.com; > > a...@ozlabs.ru; eau...@redhat.com; fel...@nutanix.com; > > jonathan.dav...@nutanix.com; changpeng....@intel.com; ken....@amd.com; > > kwankh...@nvidia.com; kevin.t...@intel.com; c...@nvidia.com; > > k...@vger.kernel.org > > Subject: Re: [PATCH 0/5] QEMU VFIO live migration > > > > On Thu, Feb 21, 2019 at 01:35:43AM +0000, Gonglei (Arei) wrote: > > > > > > > > > > -----Original Message----- > > > > From: Zhao Yan [mailto:yan.y.z...@intel.com] > > > > Sent: Thursday, February 21, 2019 8:25 AM > > > > To: Gonglei (Arei) <arei.gong...@huawei.com> > > > > Cc: alex.william...@redhat.com; qemu-devel@nongnu.org; > > > > intel-gvt-...@lists.freedesktop.org; zhengxiao...@alibaba-inc.com; > > > > yi.l....@intel.com; eskul...@redhat.com; ziye.y...@intel.com; > > > > coh...@redhat.com; shuangtai....@alibaba-inc.com; > > dgilb...@redhat.com; > > > > zhi.a.w...@intel.com; mlevi...@redhat.com; pa...@linux.ibm.com; > > > > a...@ozlabs.ru; eau...@redhat.com; fel...@nutanix.com; > > > > jonathan.dav...@nutanix.com; changpeng....@intel.com; > > ken....@amd.com; > > > > kwankh...@nvidia.com; kevin.t...@intel.com; c...@nvidia.com; > > > > k...@vger.kernel.org > > > > Subject: Re: [PATCH 0/5] QEMU VFIO live migration > > > > > > > > On Wed, Feb 20, 2019 at 11:56:01AM +0000, Gonglei (Arei) wrote: > > > > > Hi yan, > > > > > > > > > > Thanks for your work. > > > > > > > > > > I have some suggestions or questions: > > > > > > > > > > 1) Would you add msix mode support,? if not, pls add a check in > > > > vfio_pci_save_config(), likes Nvidia's solution. > > > > ok. > > > > > > > > > 2) We should start vfio devices before vcpu resumes, so we can't rely > > > > > on > > vm > > > > start change handler completely. > > > > vfio devices is by default set to running state. > > > > In the target machine, its state transition flow is > > > > running->stop->running. > > > > > > That's confusing. We should start vfio devices after vfio_load_state, > > otherwise > > > how can you keep the devices' information are the same between source side > > > and destination side? > > > > > so, your meaning is to set device state to running in the first call to > > vfio_load_state? > > > No, it should start devices after vfio_load_state and before vcpu resuming. >
What about set device state to running in load_cleanup handler ? > > > > so, maybe you can ignore the stop notification in kernel? > > > > > 3) We'd better support live migration rollback since have many failure > > > > scenarios, > > > > > register a migration notifier is a good choice. > > > > I think this patchset can also handle the failure case well. > > > > if migration failure or cancelling happens, > > > > in cleanup handler, LOGGING state is cleared. device state(running or > > > > stopped) keeps as it is). > > > > > > IIRC there're many failure paths don't calling cleanup handler. > > > > > could you take an example? > > Never mind, that's another bug I think. > > > > > then, > > > > if vm switches back to running, device state will be set to running; > > > > if vm stayes at stopped state, device state is also stopped (it has no > > > > meaning to let it in running state). > > > > Do you think so ? > > > > > > > IF the underlying state machine is complicated, > > > We should tell the canceling state to vendor driver proactively. > > > > > That makes sense. > > > > > > > 4) Four memory region for live migration is too complicated IMHO. > > > > one big region requires the sub-regions well padded. > > > > like for the first control fields, they have to be padded to 4K. > > > > the same for other data fields. > > > > Otherwise, mmap simply fails, because the start-offset and size for mmap > > > > both need to be PAGE aligned. > > > > > > > But if we don't need use mmap for control filed and device state, they are > > small basically. > > > The performance is enough using pread/pwrite. > > > > > we don't mmap control fields. but if data fields going immedately after > > control fields (e.g. just 64 bytes), we can't mmap data fields > > successfully because its start offset is 64. Therefore control fields have > > to be padded to 4k to let data fields start from 4k. > > That's the drawback of one big region holding both control and data fields. > > > > > > Also, 4 regions is clearer in my view :) > > > > > > > > > 5) About log sync, why not register log_global_start/stop in > > > > vfio_memory_listener? > > > > > > > > > > > > > > seems log_global_start/stop cannot be iterately called in pre-copy > > > > phase? > > > > for dirty pages in system memory, it's better to transfer dirty data > > > > iteratively to reduce down time, right? > > > > > > > > > > We just need invoking only once for start and stop logging. Why we need to > > call > > > them literately? See memory_listener of vhost. > > > > > > > > > > > > Regards, > > > -Gonglei > _______________________________________________ > intel-gvt-dev mailing list > intel-gvt-...@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev
