Re: [Qemu-devel] Some thoughts about per-queue iothreads in VirtIOBlock

[Paolo Bonzini]

On 20/03/2018 15:45, Edgar Kaziakhmedov wrote:
> Hi!
> 
> Recently, I have started working on the real multi-queue implementation
> for the VirtIOBlock device and came to conclusion
> that for the time being it may work only with RAW images. The reason is
> obviously lack of the true thread-safe multi-queue block
> layer, but recently I have seen the following message from Stefan
> 
> https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg04791.html
> 
> It appears like Paolo has already started implementing this feature, so
> I wonder whether the work is abandoned or not, and
> could anyone point me out to any of those patches

I have almost finished getting rid of the AioContext lock
(aio_context_acquire and aio_context_release), which is the final step
of thread-safety and a prerequisite for multiqueue.  Unfortunately it's
stalled a bit due to all the Meltdown and Spectre mess, which yes is
still going on after some months. :(

> As I understood from
> Stefan description, it is expected to change significantly
> the approach we use to interact with BlockDriverState.

I don't think the change is very large actually, at least for on-disk
devices.  I haven't yet considered network devices such as libiscsi or ceph.

Paolo