Xen users - Dec 2005 - Limiting number of CPU for Dom0.

Hi,

1. Is is possible to limit the number of CPU available to Domain0?
I''ve got Tyan 8221 motherboard, two dual core Opteron 280,
with xen-3.0 32bit installed and four domains.
I''d like to make the following CPU assignment:
Dom0: cpu=0-2
Dom1: cpu=3
Dom2: cpu=3
Dom3: cpu=3.

I tried to use:
        xm vcpu-set Domain-0 3
command, but with no luck.
Is there something like boot param for number of CPU?

2. I tried to walk around #1 problem with vcpu-pin command:
xm vcpu-pin Domain-0 0 0
xm vcpu-pin Domain-0 1 1
xm vcpu-pin Domain-0 2 2
xm vcpu-pin Domain-0 3 0-2
#(now, the last CPU should be unassigned, so lets pin it to DomUs)
xm vcpu-pin Dom1 0 3
xm vcpu-pin Dom2 0 3
xm vcpu-pin Dom3 0 3

but I''ve experienced a major slowdown, a very high CPU system
utilization (40-50%) in Dom0, and the following entries in kernel.log
near every hour:
Dec 12 12:45:21 host [177113.460002] Timer ISR/3: Time went backwards:
delta=-2658 cpu_delta=-2658 shadow=177112460744268 off=999253612
processed=177113460000000 cpu_processed=177113460000000
Dec 12 12:45:21 host [177113.460010]  0: 177113460000000
Dec 12 12:45:21 host [177113.460013]  1: 177113430000000
Dec 12 12:45:21 host [177113.460015]  2: 177113450000000
Dec 12 12:45:21 host [177113.460017]  3: 177113460000000

Thanks for reply,
--
Marcin

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> 1. Is is possible to limit the number of CPU available to Domain0?
> I''ve got Tyan 8221 motherboard, two dual core Opteron 280, 
> with xen-3.0 32bit installed and four domains.
> I''d like to make the following CPU assignment:
> Dom0: cpu=0-2
> Dom1: cpu=3
> Dom2: cpu=3
> Dom3: cpu=3.
> 
> I tried to use:
>         xm vcpu-set Domain-0 3
> command, but with no luck.
That command should work. Alternatively, just edit your xend-config.sxp
to set dom0-num-cpus
> Is there something like boot param for number of CPU?
On the linux command line you can set "maxcpus=3."

Ian

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