Re: [PATCH v4 4/4] virtio-blk: add iothread-vq-mapping parameter

[Stefan Hajnoczi]

On Thu, Dec 21, 2023 at 02:10:20PM +0100, Kevin Wolf wrote:
> Am 20.12.2023 um 14:47 hat Stefan Hajnoczi geschrieben:
> > Add the iothread-vq-mapping parameter to assign virtqueues to IOThreads.
> > Store the vq:AioContext mapping in the new struct
> > VirtIOBlockDataPlane->vq_aio_context[] field and refactor the code to
> > use the per-vq AioContext instead of the BlockDriverState's AioContext.
> > 
> > Reimplement --device virtio-blk-pci,iothread= and non-IOThread mode by
> > assigning all virtqueues to the IOThread and main loop's AioContext in
> > vq_aio_context[], respectively.
> > 
> > The comment in struct VirtIOBlockDataPlane about EventNotifiers is
> > stale. Remove it.
> > 
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> I'm looking at virtio_blk_dma_restart_cb/bh(). It seems to run all
> queued requests in the iothread of the first vq, but when the requests
> complete, they will push the result to their original vq.
> 
> Do we know that the dataplane isn't started and won't be started until
> the requests complete? (I wouldn't expect so, because then moving to the
> AioContext of the BlockBackend wouldn't have been necessary either.) Or
> is there another reason why this is safe?

You are right. I overlooked this. I'll send a patch to make s->rq
multi-queue safe.

Stefan

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