Re: [PATCH vfio 0/9] Add chunk mode support for mlx5 driver

[Leon Romanovsky <leon@kernel.org>]

On Wed, Sep 27, 2023 at 04:10:23PM -0600, Alex Williamson wrote:
> On Wed, 27 Sep 2023 13:59:06 +0300
> Yishai Hadas <yishaih@nvidia.com> wrote:
> 
> > On 20/09/2023 21:31, Jason Gunthorpe wrote:
> > > On Mon, Sep 11, 2023 at 12:38:47PM +0300, Yishai Hadas wrote:  
> > >> This series adds 'chunk mode' support for mlx5 driver upon the migration
> > >> flow.
> > >>
> > >> Before this series, we were limited to 4GB state size, as of the 4 bytes
> > >> max value based on the device specification for the query/save/load
> > >> commands.
> > >>
> > >> Once the device supports 'chunk mode' the driver can support state size
> > >> which is larger than 4GB.
> > >>
> > >> In that case, the device has the capability to split a single image to
> > >> multiple chunks as long as the software provides a buffer in the minimum
> > >> size reported by the device.
> > >>
> > >> The driver should query for the minimum buffer size required using
> > >> QUERY_VHCA_MIGRATION_STATE command with the 'chunk' bit set in its
> > >> input, in that case, the output will include both the minimum buffer
> > >> size and also the remaining total size to be reported/used where it will
> > >> be applicable.
> > >>
> > >> Upon chunk mode, there may be multiple images that will be read from the
> > >> device upon STOP_COPY. The driver will read ahead from the firmware the
> > >> full state in small/optimized chunks while letting QEMU/user space read
> > >> in parallel the available data.
> > >>
> > >> The chunk buffer size is picked up based on the minimum size that
> > >> firmware requires, the total full size and some max value in the driver
> > >> code which was set to 8MB to achieve some optimized downtime in the
> > >> general case.
> > >>
> > >> With that series in place, we could migrate successfully a device state
> > >> with a larger size than 4GB, while even improving the downtime in some
> > >> scenarios.
> > >>
> > >> Note:
> > >> As the first patch should go to net/mlx5 we may need to send it as a
> > >> pull request format to VFIO to avoid conflicts before acceptance.
> > >>
> > >> Yishai
> > >>
> > >> Yishai Hadas (9):
> > >>    net/mlx5: Introduce ifc bits for migration in a chunk mode
> > >>    vfio/mlx5: Wake up the reader post of disabling the SAVING migration
> > >>      file
> > >>    vfio/mlx5: Refactor the SAVE callback to activate a work only upon an
> > >>      error
> > >>    vfio/mlx5: Enable querying state size which is > 4GB
> > >>    vfio/mlx5: Rename some stuff to match chunk mode
> > >>    vfio/mlx5: Pre-allocate chunks for the STOP_COPY phase
> > >>    vfio/mlx5: Add support for SAVING in chunk mode
> > >>    vfio/mlx5: Add support for READING in chunk mode
> > >>    vfio/mlx5: Activate the chunk mode functionality  
> > > I didn't check in great depth but this looks OK to me
> > >
> > > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>  
> > 
> > Thanks Jason
> > 
> > >
> > > I think this is a good design to start motivating more qmeu
> > > improvements, eg using io_uring as we could go further in the driver
> > > to optimize with that kind of support.
> > >
> > > Jason  
> > 
> > Alex,
> > 
> > Can we move forward with the series and send a PR for the first patch 
> > that needs to go also to net/mlx5 ?
> 
> Yeah, I don't spot any issues with it either.  Thanks,

Hi Alex,

I uploaded the first patch to shared branch, can you please pull it?
https://git.kernel.org/pub/scm/linux/kernel/git/mellanox/linux.git/log/?h=mlx5-vfio

Thanks

> 
> Alex
> 
>