Re: [Xen-devel] time still going backwards

[Tim Freeman <tfreeman@xxxxxxxxxxx>]

On Wed, 13 Oct 2004 08:25:36 +0100
Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:

> 
> If you're getting APIC errors then all other bets are off, quite
> frankly. Do you get any of these messages on a native Linux 2.4
> kernel?

I've been running the benchmark just now on native Linux, no errors,
APIC or otherwise.  I also had originally run the benchmark on native
linux with the 'nosmp' flag (to compare more readily to Xen0) and also
no errors there.

I re-ran the benchmark last night with the 8 xenU/4 physical
configuration and repeated the problem on both the XenU's on the same
physical node (it is the one the jobs are started from).  *Although*
xen0 did not exhibit the time jump.  To answer Ian's question, I am
running ntpd on each of the xen0's, perhaps that was the problem with
domain 0 jumping (but I thought ntpd only makes minuscule steps, but
ntpdate is the one that makes bigger jumps)

Then I recompiled with Ian's suggested debug patch.  It went smoothly
actually, no time errors, but still APIC errors in xm dmesg (definitely
new, since I had rebooted).

???

I am not really a super systems person (is that obvious yet? :-), but
don't APIC errors have to do with SMP a lot of the time?  And what does
APIC have to do with XenU timing issues? (does one of the new, extra
IRQs go to XenU directly?)  Can I boot xen with the noapic flag? 

Thanks for any input, I am going to continue running different
configurations (as I originally planned) and I'll see if anything else
happens.

> 
>  -- Keir
> 
> > > xm dmesg:
> > > 
> > > (XEN) APIC error on CPU0: 00(02)
> > > (XEN) APIC error on CPU1: 00(02)
> > 
> > Odd. Probably not terminal, though.
> > 
> > > Xen0 dmesg, just two error messages:
> > > Timer ISR: Time went backwards: -59799000
> > > Timer ISR: Time went backwards: -48699000
> > 
> > Interesting. So both both the xenU domains are reporting a 14s
> > skip, and dom0 is reporting a larger skip (though this may be a
> > different incident).
> 
> 
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