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

[Lukas Straub <lukasstraub2@web.de>]

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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.

Regards,
Lukas Straub

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