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Re: [Xen-users] IO performance depends on number of DomU's?

To: Xen List <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] IO performance depends on number of DomU's?
From: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
Date: Tue, 28 Apr 2009 20:31:28 +0700
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On Tue, Apr 28, 2009 at 8:22 PM, Robert Dunkley <Robert@xxxxxxxxx> wrote:
> Is it possible to dedicate one of the CPUs to Dom0 exclusively?
> Yes.
> Add this to the kernel boot line: dom0_max_vcpus=1
> Edit /etc/xen/xend-config.sxp  -  set “(dom0-cpus 1)”
> Reboot Dom0

Some additional info :
- you might also want this line on kernel boot line :dom0_vcpus_pin.
This would ensure that dom0's vcpu 0 (the active one if it only uses
one vcpu) is assigned on physical cpu 0 (or core 0 on multicore
- those steps does not actually dedicate one CPU to dom0 exclusively.
What it does is it LIMITS dom0 to only use one CPU. To assign it
exclusively, you also need to tell domUs to NOT use that particular
CPU. Something like 'cpus="1-7"' (for 8-core system) on domU config
would tell it to NOT use core 0.However since current xen scheduler is
smart enough to assign cpu dynamically you might see the same result
with only the above config if your system load is low enough.
- to achive the same effect on your current session only without the
need to reboot:
xm vcpu-set 0 1
xm vcpu-pin 0 0 0



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