linux-kernel - Re: ublk-qcow2: ublk-qcow2 is available

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Date:   Thu, 13 Oct 2022 09:50:55 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Stefan Hajnoczi <stefanha@...il.com>
Cc:     "Richard W.M. Jones" <rjones@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        io-uring@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Kirill Tkhai <kirill.tkhai@...nvz.org>,
        Manuel Bentele <development@...uel-bentele.de>,
        qemu-devel@...gnu.org, Kevin Wolf <kwolf@...hat.com>,
        Xie Yongji <xieyongji@...edance.com>,
        "Denis V. Lunev" <den@...nvz.org>,
        Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: ublk-qcow2: ublk-qcow2 is available

On Wed, Oct 12, 2022 at 10:15:28AM -0400, Stefan Hajnoczi wrote:
> On Thu, 6 Oct 2022 at 06:14, Richard W.M. Jones <rjones@...hat.com> wrote:
> >
> > On Tue, Oct 04, 2022 at 09:53:32AM -0400, Stefan Hajnoczi wrote:
> > > qemu-nbd doesn't use io_uring to handle the backend IO,
> >
> > Would this be fixed by your (not yet upstream) libblkio driver for
> > qemu?
> 
> I was wrong, qemu-nbd has syntax to use io_uring:
> 
>   $ qemu-nbd ... --image-opts driver=file,filename=test.img,aio=io_uring

Yeah, I saw the option, previously when I tried io_uring via:

qemu-nbd -c /dev/nbd11 -n --aio=io_uring $my_file

It complains that 'qemu-nbd: Invalid aio mode 'io_uring'' even though
that 'qemu-nbd --help' does say that io_uring is supported.

Today just tried it on Fedora 37, looks it starts working with
--aio=io_uring, but the IOPS is basically same with --aio=native, and
IO trace shows that io_uring is used by qemu-nbd.


Thanks,
Ming