Re: xennet performance collapses with multiple vCPU

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Apr 13, 2020 at 06:16:59PM +0200, Manuel Bouyer wrote:
> Hello,
> 
> On Mon, Apr 13, 2020 at 04:01:39PM +0000, Andrew Doran wrote:
> > [...]
> > This confirms my suspicion and is why I wanted to play with HZ.  I think
> > soft interrupt processing is being driven off the clock interrupt.  Maybe
> > hardware interrupt processing but I think that's less likely.  Native x86
> > configured the same way does not behave like this.  Hmm.  I will play around
> > with it some more.
> 
> I did some checks in this area; including KASSERT() in idle_block() that
> that ci_ipending is 0 before and after sleeping.
> 
> I wonder if it could be an issue with IPIs instead.

Adding timestamps to differents events and lowering HZ to 20, I see that it
is the xennet's event which is delivered late. IPIs and softints works
as expected. So it seems that the topology change interracts with events
in some way.

Still investigating ...

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--