SCHED_ULE vs SCHED_4BSD for XENHVM domU
Mr. Olli
mister.olli at googlemail.com
Fri Oct 30 09:30:47 UTC 2009
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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