Re: [Xen-users] VCPU amount

[Vladislav Karpenko <vladislav@xxxxxxxxxxxxxx>]

Dear Fajar A. Nugraha

please comment my mind:

so as i understand:

1. If i have only one domU and make 2 configs for it with vcpu=1 and  
vcpu 8, the domu will have same perfomance, yes?
2. if i have 2 domu, one with vcpu=4 and second with vcpu=1, they will  
have same perfomance if one of them is idle, and half of perfomance if  
they are both loaded?
3. the only way to limit load is cpu_cap and for QOS is cpu_weight?

3. May be you mistake with:

> In theory you can have something like a domU with vcpu=7 (note that
> dom0 should have it's own dedicated core),  cpu_weight=65000, and
> cpu_cap=1, which should create a high-priority (cpu-wise) 7-way system
> whose total performance equals to that of one cpu. It could be handy
> for testing multi-threaded application to see how it performs in a
> fast CPU vs many slow CPUs.

cpu_cap=1 - the system will have only 1% of 1 cpu power, may be mast  
be cpu_cap=x*100 (x is a number of cpu for domu) for high-priority  
(cpu-wise) %x-way system
ThankU!!!

PS sorry for my english


26 ÃÃÃÃÃ 2009, Ã 00:53, Fajar A. Nugraha ÃÃÃÃÃÃÃ(Ã):

> 2009/3/26 Vladislav Karpenko <vladislav@xxxxxxxxxxxxxx>:
> > So there is two ways for domu cpu management vcpu and  cpu_weight,  
> > what is
> > the difference?
> Three actually, with cpu_weight.
> http://wiki.xensource.com/xenwiki/CreditScheduler
>
> vcpu is the number of cpu on domU. If you have lots of cores and small
> number of domUs, you might want to put each on a dedicated core (which
> is similar to how Sun's LDOM work).
>
> cpu_weight determines which domain will get higher priority when
> fighting over the same cpu, while cpu_cap is max amount of cpu
> resource it can use.
>
> In theory you can have something like a domU with vcpu=7 (note that
> dom0 should have it's own dedicated core),  cpu_weight=65000, and
> cpu_cap=1, which should create a high-priority (cpu-wise) 7-way system
> whose total performance equals to that of one cpu. It could be handy
> for testing multi-threaded application to see how it performs in a
> fast CPU vs many slow CPUs.
>
> Don't forget to check whether your xen version supports cpu_cap with
> "xm create --help_config | grep cpu"
>
> Regards,
>
> Fajar

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