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 11:51:34PM +0800, lei yang wrote:
>    On Fri, May 21, 2010 at 11:46 PM, Pasi Kärkkäinen <[1]pasik@xxxxxx> wrote:
> 
>      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][2]keir.fraser@xxxxxxxxxxxxx> wrote:
>      >
>      >      On 21/05/2010 04:09, "lei yang" <[2][3]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 I don't use "xm vcpu-pin" does it will use core 0 1 2 3 by default not
>    can use 3 4 5 6?
>

Yes, it'll use 0 1 2 3 as a default. It cannot be changed, unless you do 
custom pinning after the system has started.

>    if so, does core 0-4 just can used by dom0? domU can't use it?
> 

domU can (and will) use them, so you need to also pin the domUs so that they 
won't
try to use the dom0 cores, if you absolutely want to dedicate 4 cores only for 
dom0.

Just play with "xm vcpu-pin" and "xm vcpu-list" and you'll figure it out.

-- Pasi

>    Thanks
>    Lei
> 
> 
>      >    if remove "dom0_vcpus_pin" just use "  dom0_max_vcpus=4 " can it be
>      3 4 5
>      >    6 ?
>      >
> 
>      Yes, set up the pinning yourself.
> 
> 
>    again. if just use "dom0_max_vcpus=4" not use "dom0_vcpus_pin"  and I
>    don't use "xm vcpu-pin", can 't be 3 4 5 6,
> 
>    Thanks
>    Lei
> 
> 
>      -- 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:[4]keir.fraser@xxxxxxxxxxxxx
>      >    2. mailto:[5]yanglei.fage@xxxxxxxxx
>      > _______________________________________________
>      > Xen-devel mailing list
>      > [6]Xen-devel@xxxxxxxxxxxxxxxxxxx
>      > [7]http://lists.xensource.com/xen-devel
> 
>    --
>    "We learn from failure, not from success!"
> 
> References
> 
>    Visible links
>    1. mailto:pasik@xxxxxx
>    2. mailto:keir.fraser@xxxxxxxxxxxxx
>    3. mailto:yanglei.fage@xxxxxxxxx
>    4. mailto:keir.fraser@xxxxxxxxxxxxx
>    5. mailto:yanglei.fage@xxxxxxxxx
>    6. mailto:Xen-devel@xxxxxxxxxxxxxxxxxxx
>    7. http://lists.xensource.com/xen-devel

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