Re: [PATCH 0/2] Send all the SVQ control commands in parallel

[Hawkins Jiawei]

On Thu, 20 Apr 2023 at 01:17, Eugenio Perez Martin <eperezma@redhat.com> wrote:
>
> On Wed, Apr 19, 2023 at 1:50 PM Hawkins Jiawei <yin31149@gmail.com> wrote:
> >
> > This patchset allows QEMU to poll and check the device used buffer
> > after sending all SVQ control commands, instead of polling and checking
> > immediately after sending each SVQ control command, so that QEMU can
> > send all the SVQ control commands in parallel, which have better
> > performance improvement.
> >
> > I use vdpa_sim_net to simulate vdpa device, refactor
> > vhost_vdpa_net_load() to call vhost_vdpa_net_load_mac() 30 times,
> > refactor `net_vhost_vdpa_cvq_info.load` to call vhost_vdpa_net_load()
> > 1000 times,
>
> Maybe a little bit too high for real scenarios but it gives us a hint
> for sure :). Maybe it is more realistic to send ~10 or ~100 commands?

Yes, it is absolutely too high for real scenarios to call vhost_vdpa_net_load()
1000 times. But considering that the time to execute vhost_vdpa_net_load_mac()
30 times is very short, the result time may be highly unstable and
fluctuate greatly,
 so I call vhost_vdpa_net_load() 1000 times, hoping to get a more stable result.

>
> >  to build a test environment for sending
> > multiple SVQ control commands. Time in monotonic to
> > finish `net_vhost_vdpa_cvq_info.load`:
> >
> >     QEMU                            monotonic time
> > --------------------------------------------------
> > not patched                              89202
> > --------------------------------------------------
> > patched                                  80455
> >
>
> Is time expressed in seconds or milliseconds? I'm going to assume ms.

I got this by calling g_get_monotonic_time(), it should be microseconds
according to [1].

[1]. https://docs.gtk.org/glib/func.get_monotonic_time.html

>
> So let's say all the time was spent in the context switch between qemu
> and kernel, this is a save of (89202 - 80455)/30000 = 0.3 ms per
> command?

Yes, I think it is a save of 0.3 microseconds per command.

Thanks!

>
> Thanks!
>
> > This patchset resolves the GitLab issue at
> > https://gitlab.com/qemu-project/qemu/-/issues/1578.
> >
> > Hawkins Jiawei (2):
> >   vdpa: rename vhost_vdpa_net_cvq_add()
> >   vdpa: send CVQ state load commands in parallel
> >
> >  net/vhost-vdpa.c | 150 +++++++++++++++++++++++++++++++++++------------
> >  1 file changed, 112 insertions(+), 38 deletions(-)
> >
> > --
> > 2.25.1
> >
>