Re: [PATCH v2 0/2] virtio-blk: add iothread-vq-mapping parameter

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Sep 18, 2023 at 12:16:02PM -0400, Stefan Hajnoczi wrote:
> virtio-blk and virtio-scsi devices need a way to specify the mapping between
> IOThreads and virtqueues. At the moment all virtqueues are assigned to a single
> IOThread or the main loop. This single thread can be a CPU bottleneck, so it is
> necessary to allow finer-grained assignment to spread the load. With this
> series applied, "pidstat -t 1" shows that guests with -smp 2 or higher are able
> to exploit multiple IOThreads.
> 
> This series introduces command-line syntax for the new iothread-vq-mapping
> property is as follows:
> 
>   --device '{"driver":"virtio-blk-pci","iothread-vq-mapping":[{"iothread":"iothread0","vqs":[0,1,2]},...]},...'
> 
> IOThreads are specified by name and virtqueues are specified by 0-based
> index.
> 
> It will be common to simply assign virtqueues round-robin across a set
> of IOThreads. A convenient syntax that does not require specifying
> individual virtqueue indices is available:
> 
>   --device '{"driver":"virtio-blk-pci","iothread-vq-mapping":[{"iothread":"iothread0"},{"iothread":"iothread1"},...]},...'
> 
> There is no way to reassign virtqueues at runtime and I expect that to be a
> very rare requirement.
> 
> Note that JSON --device syntax is required for the iothread-vq-mapping
> parameter because it's non-scalar.
> 
> Based-on: 20230912231037.826804-1-stefanha@redhat.com ("[PATCH v3 0/5] block-backend: process I/O in the current AioContext")


Acked-by: Michael S. Tsirkin <mst@redhat.com>

More of a block thingy so pls use that tree.

> Stefan Hajnoczi (2):
>   qdev: add IOThreadVirtQueueMappingList property type
>   virtio-blk: add iothread-vq-mapping parameter
> 
>  qapi/virtio.json                    |  30 +++++
>  hw/block/dataplane/virtio-blk.h     |   3 +
>  include/hw/qdev-properties-system.h |   4 +
>  include/hw/virtio/virtio-blk.h      |   2 +
>  hw/block/dataplane/virtio-blk.c     | 163 +++++++++++++++++++++-------
>  hw/block/virtio-blk.c               |  92 ++++++++++++++--
>  hw/core/qdev-properties-system.c    |  47 ++++++++
>  7 files changed, 287 insertions(+), 54 deletions(-)
> 
> -- 
> 2.41.0