Re: [PATCH 1/2] block/export: add vhost-user-blk multi-queue support

[Markus Armbruster]

Stefan Hajnoczi <stefanha@redhat.com> writes:

> Allow the number of queues to be configured using --export
> vhost-user-blk,num-queues=N. This setting should match the QEMU --device
> vhost-user-blk-pci,num-queues=N setting but QEMU vhost-user-blk.c lowers
> its own value if the vhost-user-blk backend offers fewer queues than
> QEMU.
>
> The vhost-user-blk-server.c code is already capable of multi-queue. All
> virtqueue processing runs in the same AioContext. No new locking is
> needed.
>
> Add the num-queues=N option and set the VIRTIO_BLK_F_MQ feature bit.
> Note that the feature bit only announces the presence of the num_queues
> configuration space field. It does not promise that there is more than 1
> virtqueue, so we can set it unconditionally.
>
> I tested multi-queue by running a random read fio test with numjobs=4 on
> an -smp 4 guest. After the benchmark finished the guest /proc/interrupts
> file showed activity on all 4 virtio-blk MSI-X. The /sys/block/vda/mq/
> directory shows that Linux blk-mq has 4 queues configured.
>
> An automated test is included in the next commit.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  qapi/block-export.json               |  6 +++++-
>  block/export/vhost-user-blk-server.c | 24 ++++++++++++++++++------
>  2 files changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/qapi/block-export.json b/qapi/block-export.json
> index a793e34af9..17020de257 100644
> --- a/qapi/block-export.json
> +++ b/qapi/block-export.json
> @@ -93,11 +93,15 @@
>  #        SocketAddress types are supported. Passed fds must be UNIX domain
>  #        sockets.
>  # @logical-block-size: Logical block size in bytes. Defaults to 512 bytes.
> +# @num-queues: Number of request virtqueues. Must be greater than 0. Defaults
> +#              to 1.
>  #
>  # Since: 5.2
>  ##
>  { 'struct': 'BlockExportOptionsVhostUserBlk',
> -  'data': { 'addr': 'SocketAddress', '*logical-block-size': 'size' } }
> +  'data': { 'addr': 'SocketAddress',
> +         '*logical-block-size': 'size',

Tab damage.

> +            '*num-queues': 'uint16'} }

Out of curiosity: what made you pick 16 bit signed?  net.json uses both
32 and 64 bit signed.  Odd...

>  
>  ##
>  # @NbdServerAddOptions:

Acked-by: Markus Armbruster <armbru@redhat.com>