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Re: Dom0 bad network performance

Hello Jaromir,

Am 13.02.21 um 22:14 schrieb Jaromír Doleček:
There is one other thing that I remembered from last time I was looking at this.

IIRC it's just the network performance Dom0 <-> outside which was slow
compared to native, for DomU (running on that Dom0) <-> outside it was
line-speed nevertheless for me.

Perhaps then this is a red herring, and not really worth investigating
- you will not really be running anything directly on the Dom0.

If that were the case, then I would be able to live with it because I see it the same way as you - in Dom0, the network speed is not so important to me. However, even in the DomU's no better performance is retrievable - regardless of whether the DomU is a NetBSD 9.1 stable or a NetBSD current. My comparison measurement with iperf brought it to almost identical values around 25 MB/s for NetBSD 9.1 Stable. The values for NetBSD-current were noticeably lower at ~18 MB/s.

peterma@nuc:~> iperf3 -w 128K -c
Connecting to host, port 5201
[  5] local port 35990 connected to port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[ 5] 0.00-1.00 sec 25.5 MBytes 214 Mbits/sec 0 164 KBytes [ 5] 1.00-2.00 sec 26.8 MBytes 225 Mbits/sec 7 192 KBytes
[  5]   2.00-3.00   sec  26.3 MBytes   221 Mbits/sec   26    151 KBytes

> There are a bunch of optimizations particularly in pmap, which are
> disabled on Dom0 kernel compared to the native one. It also needs to
> do MMU updates via Xen hypercalls. So it will always be somewhat
> slower than native.

Well, maybe my combination of low-end CPU and NetBSD 9.1 Dom0 without SMP is actually the decisive factor that makes the lack of optimizations particularly noticeable here. I still have a little hope that maybe it's just a setting thing in the network stack? During the test, the CPU is 80% idle, so would have reserves.

Kind regards

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