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

[Lukas Straub]

On Mon, 27 Apr 2020 11:34:32 +0100
"Dr. David Alan Gilbert" <address@hidden> wrote:

> * Lukas Straub (address@hidden) wrote:
> > On Sat, 11 Apr 2020 19:16:54 +0200
> > Lukas Straub <address@hidden> 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?

No.

> Dave
> 
> > 
> > Regards,
> > Lukas Straub  
> 
> 
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
>

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