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

[Nikita Lebedev <darth@xxxxxxxxxxxx>]

Jan Marquardt пишет:
> 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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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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