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

[Jan Marquardt <jm@xxxxxxxxxxx>]

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

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