On 24/11/2022 19:39, Yishai Hadas wrote:
This series adds migration PRE_COPY uAPIs and their implementation as
part of mlx5 driver.
The uAPIs follow some discussion that was done in the mailing list [1]
in this area.
By the time the patches were sent, there was no driver implementation
for the uAPIs, now we have it for mlx5 driver.
The optional PRE_COPY state opens the saving data transfer FD before
reaching STOP_COPY and allows the device to dirty track the internal
state changes with the general idea to reduce the volume of data
transferred in the STOP_COPY stage.
While in PRE_COPY the device remains RUNNING, but the saving FD is open.
A new ioctl VFIO_MIG_GET_PRECOPY_INFO is provided to allow userspace to
query the progress of the precopy operation in the driver with the idea
it will judge to move to STOP_COPY at least once the initial data set is
transferred, and possibly after the dirty size has shrunk appropriately.
User space can detect whether PRE_COPY is supported for a given device
by checking the VFIO_MIGRATION_PRE_COPY flag once using the
VFIO_DEVICE_FEATURE_MIGRATION ioctl.
Extra details exist as part of the specific uAPI patch from the series.
Finally, we come with mlx5 implementation based on its device
specification for PRE_COPY.
To support PRE_COPY, mlx5 driver is transferring multiple states
(images) of the device. e.g.: the source VF can save and transfer
multiple states, and the target VF will load them by that order.
The device is saving three kinds of states:
1) Initial state - when the device moves to PRE_COPY state.
2) Middle state - during PRE_COPY phase via VFIO_MIG_GET_PRECOPY_INFO,
can be multiple such states.
3) Final state - when the device moves to STOP_COPY state.
After moving to PRE_COPY state, the user is holding the saving FD and
should use it for transferring the data from the source to the target
while the VM is still running. From user point of view, it's a stream of
data, however, from mlx5 driver point of view it includes multiple
images/states. For that, it sets some headers with metadata on the
source to be parsed on the target.
At some point, user may switch the device state from PRE_COPY to
STOP_COPY, this will invoke saving of the final state.
As discussed earlier in the mailing list, the data that is returned as
part of PRE_COPY is not required to have any bearing relative to the
data size available during the STOP_COPY phase.
For this, we have the VFIO_DEVICE_FEATURE_MIG_DATA_SIZE option.
In mlx5 driver we could gain with this series about 20-30 percent
improvement in the downtime compared to the previous code when PRE_COPY
wasn't supported.
The series includes some pre-patches to be ready for managing multiple
images then it comes with the PRE_COPY implementation itself.
The matching qemu changes can be previewed here [2].
They come on top of the v2 migration protocol patches that were sent
already to the mailing list.
Note:
As this series includes a net/mlx5 patch, we may need to send it as a
pull request format to VFIO to avoid conflicts before acceptance.
[1] https://lore.kernel.org/kvm/20220302172903.1995-8-shameerali.kolothum.thodi@xxxxxxxxxx/
[2] https://github.com/avihai1122/qemu/commits/mig_v2_precopy
Changes from V0: https://www.spinics.net/lists/kvm/msg294247.html
Drop the first 2 patches that Alex merged already.
Refactor mlx5 implementation based on Jason's comments on V0, it includes
the below:
* Refactor the PD usage to be aligned with the migration file life cycle.
* Refactor the MKEY usage to be aligned with the migration file life cycle.
* Refactor the migration file state.
* Use queue based data chunks to simplify the driver code.
* Use the FSM model on the target to simplify the driver code.
* Extend the driver pre_copy header for future use.
Yishai
Jason Gunthorpe (1):
vfio: Extend the device migration protocol with PRE_COPY
Shay Drory (3):
net/mlx5: Introduce ifc bits for pre_copy
vfio/mlx5: Fallback to STOP_COPY upon specific PRE_COPY error
vfio/mlx5: Enable MIGRATION_PRE_COPY flag
Yishai Hadas (10):
vfio/mlx5: Enforce a single SAVE command at a time
vfio/mlx5: Refactor PD usage
vfio/mlx5: Refactor MKEY usage
vfio/mlx5: Refactor migration file state
vfio/mlx5: Refactor to use queue based data chunks
vfio/mlx5: Introduce device transitions of PRE_COPY
vfio/mlx5: Introduce SW headers for migration states
vfio/mlx5: Introduce vfio precopy ioctl implementation
vfio/mlx5: Consider temporary end of stream as part of PRE_COPY
vfio/mlx5: Introduce multiple loads
drivers/vfio/pci/mlx5/cmd.c | 408 ++++++++++++++----
drivers/vfio/pci/mlx5/cmd.h | 93 ++++-
drivers/vfio/pci/mlx5/main.c | 750 ++++++++++++++++++++++++++++------
drivers/vfio/vfio_main.c | 74 +++-
include/linux/mlx5/mlx5_ifc.h | 14 +-
include/uapi/linux/vfio.h | 122 +++++-
6 files changed, 1241 insertions(+), 220 deletions(-)
Hi Alex,
Any comments on V1 ? I would like to send V2 very soon with a small fix
that was found in patch #9 (see my note in the list).
As no comments were published on the UAPI patch so far and the other
code is mlx5 driver specific, I believe that V2 can be a merge candidate.
Let's try to complete review soon so that we can send a PR for the first
net/mlx5 patch, the others should go later on via the vfio tree.
By that, we can have in kernel 6.2 feature complete for migration V2 in
the UAPI area that were in V1 and we can focus on completing the QEMU side.
Thanks,
Yishai
