RE: [Xen-users] big latency, packet losses with HVM guests

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: Tomasz Chmielewski [mailto:mangoo@xxxxxxxx] 
> Sent: 30 November 2006 14:46
> To: Petersson, Mats
> Cc: Tomasz Chmielewski; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-users] big latency, packet losses with HVM guests
> 
> > You may find that if you can run one CPU for Dom0 and 
> another for DomU
> > (say in a dual core system), you may get better performance 
> than if you
> > run both CPU's for both Dom0 and DomU.
> 
> One CPU of dom0 should be enough.
> How can I start dom0 on just one CPU? Some option passed via 
> grub maybe?
> 
> Because setting "(dom0-cpus 1)" in xend-config.sxp doesn't 
> seem to work:
> 
> # xm dmesg|grep CPU
> (XEN) Initializing CPU#0
> (XEN) CPU: L1 I cache: 32K, L1 D cache: 32K
> (XEN) CPU: L2 cache: 2048K
> (XEN) CPU: Physical Processor ID: 0
> (XEN) CPU: Processor Core ID: 0
> (XEN) Intel machine check reporting enabled on CPU#0.
> (XEN) CPU0: Intel(R) Xeon(R) CPU            3050  @ 2.13GHz 
> stepping 06
> (XEN) Initializing CPU#1
> (XEN) CPU: L1 I cache: 32K, L1 D cache: 32K
> (XEN) CPU: L2 cache: 2048K
> (XEN) CPU: Physical Processor ID: 0
> (XEN) CPU: Processor Core ID: 1
> (XEN) Intel machine check reporting enabled on CPU#1.
> (XEN) CPU1: Intel(R) Xeon(R) CPU            3050  @ 2.13GHz 
> stepping 06
> (XEN) checking TSC synchronization across 2 CPUs: passed.
> (XEN) Brought up 2 CPUs
> (XEN) Dom0 has maximum 2 VCPUs
> 
> 
> Or perhaps it won't work with dual-core CPUs (it's really one CPU)?

Well, it's only one CPU in the sense that it occupies one socket, rather
than the number of actual "Central Processing Units" it uses. In fact
some of the early Intel ones are even separate chips mounted in one
package - but either way, there is definitely two separate units, so the
OS should behave just like if you have two sockets for two single-core
CPU's [except for the NUMA awareness and some other things where the
"which socket this is matters"]. 

You can use "xm vcpu-set 0 1" to set the number of CPU's in Dom0. And
you probably also want to use "xm vcpu-pin 0 0 0" to force the first
core to be Dom0, and "xm vcpu-pin <domu-id> 0 1" to set the second
domain to run on the second core. 

--
Mats
> 
> 
> 
> -- 
> Tomasz Chmielewski
> http://wpkg.org
> 
> 
> 
> 
> 



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