Re: [Qemu-devel] [PATCH 5/7] coroutine: rewrite pool to avoid mutex

[Kevin Wolf <kwolf@redhat.com>]

Am 28.11.2014 um 18:31 hat Paolo Bonzini geschrieben:
> 
> 
> On 28/11/2014 17:40, Kevin Wolf wrote:
> >> > I still believe we will end with some kind of coroutine bypass scheme
> >> > (even coroutines _do_ allocate an AIOCB, so calling bdrv_aio_readv
> >> > directly can help), but hey it cannot hurt to optimize hot code.
> >
> > Not sure if speculations about the future belong into commit messages,
> > but while it may turn out that a bypass is required in the end (I hope
> > it doesn't), the part about AIOCBs is wrong if you really consistently
> > use coroutines all the way down from the device to the block driver.
> 
> This is much harder for virtio-scsi than for virtio-blk, though.

Why is that? At least replacing the bdrv_aio_*() call by
coroutine_create/coroutine_enter/bdrv_co_*() is a mechanical change that
shouldn't be any harder for virtio-scsi. Whether we can optimise even
more by integration the device more with coroutines might be a different
problem, but at this point you've already got rid of AIOCBs.

Kevin