Re: colo: qemu 4.2.0 vs. qemu 5.0.0-rc2 performance regression

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Lukas Straub (lukasstraub2@web.de) wrote:
> On Sat, 11 Apr 2020 19:16:54 +0200
> Lukas Straub <lukasstraub2@web.de> wrote:
> 
> > Hello Everyone,
> > I did some Benchmarking with iperf3 and memtester (to dirty some guest memory)
> > of colo performance in qemu 4.2.0 and in qemu 5.0.0-rc2
> > with my bugfixes on top.( https://lists.nongnu.org/archive/html/qemu-devel/2020-04/msg01432.html )
> > 
> > I have taken the average over 4 runs.
> > Client-to-server tcp bandwidth rose slightly from ~83.98 Mbit/s to ~89.40 Mbits.
> > Server-to-client tcp bandwidth fell from ~9.73 Mbit/s to ~1.79 Mbit/s.
> > Client-to-server udp bandwidth stayed the same at 1.05 Mbit/s
> > and jitter rose from ~5.12 ms to ~10.77 ms.
> > Server-to-client udp bandwidth fell from ~380.5 Kbit/s to ~33.6 Kbit/s
> > and jitter rose from ~41.74 ms to ~83976.15 ms (!).
> > 
> > I haven't looked closely into it, but i think
> > 0393031a16735835a441b6d6e0495a1bd14adb90 "COLO: Optimize memory back-up process"
> > is the culprint as it reduces vm downtime for the checkpoints but increases
> > the overall checkpoint time and we can only release miscompared primary packets
> > after the checkpoint is completely finished.
> > 
> > Another thing that I noticed: With 4.2.0, the secondary qemu uses thrice
> > the amount of gest memory. With 5.0.0-rc2 it's just double the amount of
> > guest memory. So maybe the ram cache isn't working properly?
> > 
> > Regards,
> > Lukas Straub
> 
> Hmm,
> I looked at my test again and saw that the results where very noisy, so qemu 5.0.0-rc2
> being slower was just a coincidence. I did increase the test time and the results are 
> more meaningful now. Now qemu 5.0.0-rc2 is around the same speed and still faster
> in the client-to-server tcp case.
> 
> Sorry for the noise.

Is it back to using 3x RAM in the secondary?

Dave

> 
> Regards,
> Lukas Straub


--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK