On Wed, 2004-10-13 at 15:00, Tim Freeman wrote:
> 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)
ntp can make large corrections, however the standard setup (default) is
to make ~120ms changes per "tick" on checking. Once ntpd is synced up it
shouldn't need to make more than ~2ms of change per tick unless your
hardware clock is totally farked (I'd call 1ms in 60 seconds beyond
farked to be honest). :)
>
> 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?
Originally from what I understand, APIC was inplemented to allow SMP,
and as such was only used for SMP. Some time around the middle of the
2.4 series I noticed that you could select UP-APIC when SMP was
disabled. Not certain exactly when that ability was enabled though.
>
>
> 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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