RE: [Xen-users] Xen 3.2 with Ubuntu 8.04 (64-Bit) on Intel Nehalem (i7)

[Nathan Eisenberg <nathan@xxxxxxxxxxxxxxxx>]

The new Nehalem implementation of HT is significantly improved over the Pentium 
4 version of it.  Personally, I would lean towards leaving it on.  However, it 
should be pretty trivial for you to do some benchmarks and figure out what 
gives the best result in your configuration.

Thank You,
Nathan Eisenberg
Sr. Systems Administrator
Atlas Networks, LLC
Atlas Networks is an Atlas Accelerator Company 


-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Nikita Lebedev
Sent: Wednesday, May 27, 2009 2:18 AM
To: Jan Marquardt
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Xen 3.2 with Ubuntu 8.04 (64-Bit) on Intel Nehalem (i7)

Jan Marquardt ÐÐÑÐÑ:
> Hallo list,
>
> i am testing a Dell M610 with two quadcore Intel Nehalem CPUs at the
> moment, so with Hyper-Threading 16 cores in total. As mentioned in the
> subject I am using Ubuntu 8.04 64Bit and Xen 3.2 from Ubuntu package.
> During these tests I hit on some issues, which are not clear to me. I
> would be thankful for any comments/hints/thoughts on the following
> topics:
>
> 1. I recognized that CONFIG_NR_CPUS is set to 8 in the Ubuntu Xen
> kernel. However, the Ubuntu server kernel has a limitation of 64. Is
> there any specific reason for the limitation of 8 in the Xen kernel?
>
> 2. After recompiling the kernel with CONFIG_NR_CPUS=16 /proc/cpuinfo
> still just shows 8 cores, but xm vcpu-list shows the 16 cores
> correctly. Does someone know which config options are necessary to get
> it working correctly?
>
> 3. As you may know the Nehalem cpus support Hyper Threading again. Is
> it    recommendable/useful to treat the logical cores like the
> physical cores? In our case we always assign one core only once to one
> domu to guarantee the performance to our customers. So the main
> question is if the performance differs between physical and logical
> cores noticeable.
>
> Kind regards,
>
> Jan Marquardt
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
AFAIK HT technology decrease VM performance. VMware strongly recommends
to disable HT on servers, which runs VMware ESX server, I think that Xen
is familar to ESX, so HT will decrease performance on Xen too.

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