Re: Dom0 bad network performance

[Jaromír Doleček <jaromir.dolecek%gmail.com@localhost>]

Le sam. 13 févr. 2021 à 19:42, Greg Troxel <gdt%lexort.com@localhost> a écrit :
> > - "correct ACK header predictions" and "correct data packet header
> > predictions" are many times higher without Xen than with Xen. Both
> > parameters don't tell me much, but they sound like a high value would
> > be beneficial here, i.e. another indication that something is wrong in
> > the case with Xen?
>
> I suspect that's not important, but it is interesting.  I see there was
> one out-of-order packet without xen, and two with.  I didn't see
> anything else in the diff that was concerning.
>
> Jaromir suggested current; netbsd-9 XEN3_DOMU uses only 1 cpu, and my
> understanding is that current runs SMP.  I'm guessing your box has a few
> not-super-fast each cores, and so that might matter a lot.

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.

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.

Jaromir