Re: Dom0 bad network performance (was: NetBSD/Xen samba performance low (compared to NetBSD/amd64))

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hi Jaromir,

Am 13.02.21 um 09:21 schrieb Jaromír Doleček:
> Le sam. 13 févr. 2021 à 09:14, Matthias Petermann <mp%petermann-it.de@localhost> a écrit :
> > This means that with a window size of 128K the difference is even more
> > significant, i.e. the speed under Xen is only a third of the speed
> > achieved with a "pure" NetBSD kernel.
>
> Can you try with NetBSD -current Xen kernel instead of 9.0?
>
> There were some changes in xennet(4) there, which improved the performance.
>
> Jaromir

I tried with both the following daily builds:

 - 
http://nycdn.netbsd.org/pub/NetBSD-daily/HEAD/202102120920Z/amd64/binary/kernel/

 - 
http://nycdn.netbsd.org/pub/NetBSD-daily/HEAD/202102081850Z/amd64/binary/kernel/netbsd-XEN3_DOM0.gz

but unfortunately this kernels do panic. The device does not have a 
serial console, so the only option I had was to film the boot sequence 
and extract frames from it. Unfortunately, they are very blurry due to 
the scrolling speed and I can only guess so much:

```
panic: kernel diagnostic assertion "!wskbd console initted" failed: file 
"/home/source/ab/HEAD/src/sys/dev/wscons/wskbd.c". line 523
cpu0: Begin traceback...
```

Is this a known issue, or could another change (USB driver? XHCI?) be 
playing into this?

However, I was able to convince the kernel to boot by forcing the use of 
com1 as console in boot.cfg (although the interface does not exist). Now 
any console output is missing, but network works and here are the test 
results with 128K window size:

```
mpeterma@nuc:~> iperf3 -w 128K -c 192.168.2.50
Connecting to host 192.168.2.50, port 5201
[  5] local 192.168.2.40 port 49112 connected to 192.168.2.50 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  61.3 MBytes   515 Mbits/sec  256   90.5 KBytes
[  5]   1.00-2.00   sec  67.4 MBytes   565 Mbits/sec  334   73.5 KBytes
[  5]   2.00-3.00   sec  65.9 MBytes   553 Mbits/sec  406    117 KBytes
[  5]   3.00-4.00   sec  62.7 MBytes   526 Mbits/sec  313   84.8 KBytes
```

--> This is an improvement by a factor of 2 compared to 9.1 :-) I did 
also test other window sizes. They did scale proportional to my tests 
with 9.1 so I leave the results out here. I also repeated a test with my 
"real" workload (sftp) and get an equivalent improvement here as well 
(10 MByte/s instead of 5 MByte/s).

I think this is going in the right direction - just wondering what 
factors influence the difference between Dom0 and the "pure" NetBSD that 
might be worth another test.

Also, I also just read your 2nd mail - I also thought that xennet 
normally should not have any impact on Dom0 performance. So it seems to 
be more the "other changes" that help me in my case. Do you have a 
suspicion which ones they could be? I'm particularly interested in 
whether these can be easily backported to 9.1_STABLE if necessary?

Kind regards & many thanks
Matthias