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

  • To: Robert Dunkley <Robert@xxxxxxxxx>
  • From: lei yang <yanglei.fage@xxxxxxxxx>
  • Date: Fri, 21 May 2010 23:38:22 +0800
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Xen Mailing List <xen-users@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Fri, 21 May 2010 08:40:05 -0700
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On Fri, May 21, 2010 at 8:02 PM, Robert Dunkley <Robert@xxxxxxxxx> wrote:

Hi Lei,



Q1: The pin is needed to lock Dom0 to cores 0 & 1.


dom0_max_vcpus=4 dom0_vcpus_pin just lock Dom0 to cores0 and 1?? but it's "4"

Q2: It means 4 vcpus are allocated to Dom0, they can float between physical cores.

dom0_max_vcpus=4 , can be the 4 cores=2 3 4 5, does it will change to 1 2 3 4? or just bind to 2 3 4 5
dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3?

VCPUs don’t really line up with cores, you can assign 8 vcpus on a DomU  on a 4 core Dom0 box for example. 8 cpus will appear in the VM but Xen will try to allocate the request within its 4 physucal cores. Generally assigning more VPUs than you have physical cores is pointless.


Q3: No SMP for a DOMU will mean the kernel is not SMP aware, this can save a small amount of overhead and improve scheduling in certain cases on a single core DOMU. I’m not sure what the affect would be on Dom0, my guess is it won’t be good.






From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of lei yang
Sent: 21 May 2010 04:09
To: Xen Mailing List; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] What's the different for "dom0_max_vcpus=4dom0_vcpus_pin" and "dom0_max_vcpus=4" ?


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

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?

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?


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