Tested pass with vhost_vdpa device's regression tests. Tested-by: Lei Yang <leiy...@redhat.com>
On Thu, May 8, 2025 at 2:47 AM Jonah Palmer <jonah.pal...@oracle.com> wrote: > > Current memory operations like pinning may take a lot of time at the > destination. Currently they are done after the source of the migration is > stopped, and before the workload is resumed at the destination. This is a > period where neigher traffic can flow, nor the VM workload can continue > (downtime). > > We can do better as we know the memory layout of the guest RAM at the > destination from the moment that all devices are initializaed. So > moving that operation allows QEMU to communicate the kernel the maps > while the workload is still running in the source, so Linux can start > mapping them. > > As a small drawback, there is a time in the initialization where QEMU > cannot respond to QMP etc. By some testing, this time is about > 0.2seconds. This may be further reduced (or increased) depending on the > vdpa driver and the platform hardware, and it is dominated by the cost > of memory pinning. > > This matches the time that we move out of the called downtime window. > The downtime is measured as checking the trace timestamp from the moment > the source suspend the device to the moment the destination starts the > eight and last virtqueue pair. For a 39G guest, it goes from ~2.2526 > secs to 2.0949. > > Future directions on top of this series may include to move more things ahead > of the migration time, like set DRIVER_OK or perform actual iterative > migration > of virtio-net devices. > > Comments are welcome. > > This series is a different approach of series [1]. As the title does not > reflect the changes anymore, please refer to the previous one to know the > series history. > > This series is based on [2], it must be applied after it. > > [Jonah Palmer] > This series was rebased after [3] was pulled in, as [3] was a prerequisite > fix for this series. > > v4: > --- > * Add memory listener unregistration to vhost_vdpa_reset_device. > * Remove memory listener unregistration from vhost_vdpa_reset_status. > > v3: > --- > * Rebase > > v2: > --- > * Move the memory listener registration to vhost_vdpa_set_owner function. > * Move the iova_tree allocation to net_vhost_vdpa_init. > > v1 at https://lists.gnu.org/archive/html/qemu-devel/2024-01/msg02136.html. > > [1] > https://patchwork.kernel.org/project/qemu-devel/cover/20231215172830.2540987-1-epere...@redhat.com/ > [2] https://lists.gnu.org/archive/html/qemu-devel/2024-01/msg05910.html > [3] > https://lore.kernel.org/qemu-devel/20250217144936.3589907-1-jonah.pal...@oracle.com/ > > Jonah - note: I'll be on vacation from May 10-19. Will respond to > comments when I return. > > Eugenio Pérez (7): > vdpa: check for iova tree initialized at net_client_start > vdpa: reorder vhost_vdpa_set_backend_cap > vdpa: set backend capabilities at vhost_vdpa_init > vdpa: add listener_registered > vdpa: reorder listener assignment > vdpa: move iova_tree allocation to net_vhost_vdpa_init > vdpa: move memory listener register to vhost_vdpa_init > > hw/virtio/vhost-vdpa.c | 107 +++++++++++++++++++++------------ > include/hw/virtio/vhost-vdpa.h | 22 ++++++- > net/vhost-vdpa.c | 34 +---------- > 3 files changed, 93 insertions(+), 70 deletions(-) > > -- > 2.43.5 >
