Oops, sorry for posting this twice. I thought it didn't go through with the first attempt.



On 29 Oct 2009, at 23:27, Carsten Heesch wrote:

Hi guys,

After FreeBSD 8.0-RC2 is working well (for me) on Xen 3.3.1, I somehow made an interesting observation:

Even if the FreeBSD domU does absolutely nothing, each of the assigned vCPUs will be reported by xentop as using 15%-25% CPU time. It doesn't matter, if domU is running with 1 or 4 vCPUs. All of them float at the same level.

On the same Xen box five other domU's (CentOS 5.2-5.4) have an idle CPU percentage of 0 to 0.5%.

So I played a bit and figured out that changing the scheduler in the XENHVM kernel configuration from "option SCHED_ULE" to "option SCHED_4BSD" resolves this problem. The idle state of the FreeBSD domU is now identical to the CentOS domU's.

However, this of course means using an old (maybe even deprecated?) scheduler, which moreover isn't the best choice for multiple (virtual) CPUs.

The configuration I tested on is:
Intel i7 920 Quad-Core with Hyperthreading (8 logical CPUs)
Citrix XenServer 5.5 (based on CentOS 5.2, Xen 3.3.1)


Any thoughts, ideas, solutions?


Thanks!

Carsten


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Best regards,

Carsten Heesch

Mobile: +44 (0)7889-129998
Mail:   cars...@heesch.me.uk
Skype:  carstenh74



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