SCHED_ULE vs SCHED_4BSD for XENHVM domU

[Mr. Olli]

Hi,

I compiled FreeBSD8-RC2 from SVN revision 198456 with the XEN config
file left unchanged. the domU is 32bit.

I'm running on SCHED_ULE and the system consumes <1% vCPU (according to
xentop) in idle status.

My dom0 is a gentoo linux 32-bit with 2x athlonMP 1900+ and 4GB ram.

greetz,
----
Mr. Olli


On Thu, 2009-10-29 at 23:12 +0000, 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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