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Re: [Xen-users] CPU's vs. VCPUS

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] CPU's vs. VCPUS
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Sat, 6 Oct 2007 01:48:23 +0100
Cc: matthewh <matt@xxxxxxxxxxxxx>
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You can't combine CPUs to make a more powerful virtual CPU, sadly.

However, there are a flexible set of parametrs that you can use to portion 
power: you can dedicate whole cores to a domU, you can allow it to run only 
on certain cores, you can allow it to run share some cores with other 
domains, you can specify the aggregate power it gets (in terms of % of one 
CPU) per unit time.

Hopefully this will help get you where you want to go.  If there's something 
specific you want to achieve, maybe you could explain it to the list and 
somebody might have helpful ideas / comments.


On Wednesday 03 October 2007, matthewh wrote:
> Hi All,
> I am new to Xen, and would like to know if anyone can help with this
> problem I have.
> I have a dual - Quad Core Intel 5535 VT 2.66 server, with 24G ram running
> CentOS5 dom0 and domU (both 64 bit). Everything works great and I am VERY
> impressed with the efficiency of Xen (i have always been a UML man). I
> would however, like to run a single domU domain, with a single VCPU, but
> get the power of say, 7 cores, leaving 1 to the dom0 instance. First off, I
> would like to know if this is possible.
> In my config file I have specified cpus = "1-7" and vpus=1 in the hope that
> the 1 vcpu would be an almighty powerful one, but this isn't the case.
> There is no errors booting it up, and
>      [\047cpus\047, \0470-7\047]
> appears in the xend logfile.
> Here is a copy of the config file.
> name = "test1"
> builder = "hvm"
> memory = "20000"
> disk = [ 'file:/virtual/test1,hda,w', ]
> vif = [ 'type=ioemu, mac=00:16:3e:18:34:76, bridge=xenbr0', ]
> uuid = "d8a2a092-399a-ecb9-24fb-7caf66f883b2"
> device_model = "/usr/lib64/xen/bin/qemu-dm"
> kernel = "/usr/lib/xen/boot/hvmloader"
> vnc=0
> # vncunused=1
> apic=1
> acpi=1
> pae=1
> cpus="0-7"
> vcpus=1
> usb=0
> serial = "pty" # enable serial console
> on_reboot   = 'restart'
> on_crash    = 'restart'
> Any help / advice / comments and greatly appreciated.
> Regards, Matt Hanna

Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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