Re: [PATCH RFC 0/3] vdpa: dedicated descriptor table group

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On 8/9/2023 7:49 AM, Eugenio Perez Martin wrote:
On Wed, Aug 9, 2023 at 2:56 PM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> wrote:
Following patchset introduces dedicated group for descriptor table to
reduce live migration downtime when passthrough VQ is being switched
to shadow VQ. As this RFC set is to seek early feedback on the uAPI
and driver API part, for now there's no associated driver patch consuming
the API. As soon as the support is in place on both hardware device and
driver, performance data will be show using real hardware device. The
target goal of this series is to reduce the SVQ switching overhead
to less than 300ms on a ~100GB guest with 2 non-mq vhost-vdpa devices.

I would expand the cover letter with something in the line of:
The reduction in the downtime is thanks to avoiding the full remap in
the switching.
Sure, will add in the next.

The plan of the intended driver implementation is to use a dedicated
group (specifically, 2 in below table) to host descriptor table for
all data vqs, different from where buffer addresses are contained (in
group 0 as below). cvq does not have to allocate dedicated group for
descriptor table, so its buffers and descriptor table would always
belong to a same group (1).

               |  data vq | ctrl vq
vq_group      |    0     |    1
vq_desc_group |    2     |    1

Acked-by: Eugenio Pérez <eperezma@xxxxxxxxxx>



Si-Wei Liu (3):
   vdpa: introduce dedicated descriptor group for virtqueue
   vhost-vdpa: introduce descriptor group backend feature
   vhost-vdpa: uAPI to get dedicated descriptor group id

  drivers/vhost/vdpa.c             | 27 +++++++++++++++++++++++++++
  include/linux/vdpa.h             | 11 +++++++++++
  include/uapi/linux/vhost.h       |  8 ++++++++
  include/uapi/linux/vhost_types.h |  5 +++++
  4 files changed, 51 insertions(+)


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