Re: [Xen-devel] time still going backwards

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> One thing is also that on this node Xen chose to host both guests on CPU
> 1 (and I know that at the exact moment of failure Xen1 was interacting
> with the only other one not to spread out the guests (it actually had
> all three Xen0,Xen1,Xen2 on CPU 0)).  

The code that choses the initial CPU for a domain is an
embarrassment, and currently makes no attempt to distribute them
evenly. I'll check in something that at least chooses the CPU
with the smallest number of domains. Proper load balancing will
require someone to write the simple little daemon discussed
earlier this week on the list.

> 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).

Are you running ntpdate ot xntpd in domain0? What about the other
domains? (I presume that you haven't requested
independent_wallclock for them?)

It might be interesting to modify the printk in
arch/xen/i386/kernel/time.c to also print the variables that go
into the delta calculation e.g.:

printk("Timer ISR: Time went backwards: %lld %lld %ld %lld\n", delta,
shadow_system_time, (cur_timer->get_offset() * NSEC_PER_USEC), 
processed_system_time);

I presume it's shadow_system_time that's jumping, but it would be
useful if you could add debuging to prove this.

Ian


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