Re: [Xen-devel] What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, May 21, 2010 at 11:39:50PM +0800, lei yang wrote:
>    On Fri, May 21, 2010 at 2:57 PM, Keir Fraser
>    <[1]keir.fraser@xxxxxxxxxxxxx> wrote:
> 
>      On 21/05/2010 04:09, "lei yang" <[2]yanglei.fage@xxxxxxxxx> wrote:
> 
>      > Hi experts,
>      >
>      >
>      > Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and
>      > "dom0_max_vcpus=4" ? which will get better performance
> 
>      The former restricts Xen to only run Dom0 VCPUs 0-3 on physical CPUs
>      0-3.
> 
> 
>    dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3?
>

Yes.

> can it be 3 4 5 6?
>

Yes, modify the pinning when the system has booted up using "xm vcpu-pin".

>    if remove "dom0_vcpus_pin" just use "  dom0_max_vcpus=4 " can it be 3 4 5
>    6 ?
> 

Yes, set up the pinning yourself.

-- Pasi

> 
>      It's not really a performance thing, but instead is to mean that some
>      things
>      like cpufreq management can work directly from dom0. We don't really use
>      the
>      dom0_vcpus_pin option much.
>      > Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or
>      means "4
>      > cores(not dedicate cores) will be used by dom0, eg: core2-5 or
>      core3-6?
> 
>      Dom0's VCPUs can be scheduled on any physical CPU at any time, unles
>      dom0_vcpus_pin is specified.
>      > Q3.what does mean "nosmp" , xen, dom0,domU, will just use one
>      core????if so,
>      > can we specify the use different core. eg: dom0=core2 domU=core3? xen
>      will use
>      > just one core?
> 
>      It brings Xen up on the boot CPU only. Nothing in the system will use
>      the
>      other CPUs. You don't want to use this option really.
>       -- Keir
> 
>    --
>    "We learn from failure, not from success!"
> 
> References
> 
>    Visible links
>    1. mailto:keir.fraser@xxxxxxxxxxxxx
>    2. mailto:yanglei.fage@xxxxxxxxx

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