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RE: [Xen-devel] another scheduler problem, on x86_64 only?

To: "Andrew Theurer" <habanero@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] another scheduler problem, on x86_64 only?
From: "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
Date: Wed, 13 Jul 2005 09:37:53 -0700
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Thread-topic: [Xen-devel] another scheduler problem, on x86_64 only?
Andrew Theurer wrote:
> I Noticed that dom0 is only getting about 50% cpu after seeing about
> 1/2 the performance on some benchmarks, xen0 vs baremetal.  I just
> ran a quick cpu bound script:
> while [ 1 ]; do x=1; done&
> ..and I get this cpu util:
>       total   domains
>       ------- ----------
>  cpu0:  [050.7] d0-0[050.7]
>  cpu0:  [049.8] d0-0[049.8]
>  cpu0:  [049.8] d0-0[049.8]
>  cpu0:  [049.8] d0-0[049.8]
> Anyone else seen this on x86_64 dom0 with BVT?

I also see this problem. For example, if I run lmbench on dom0, I used
to see almost 100% CPU load, but it's clearly limited to <= 50% (and
performance is bad). This stared to happen when the default scheduler is
switched to sedf. I also tried various parameters with sedf, the results
were basically same, i.e. never got > 50%. To me it looks like the
scheduler is always giving 50% CPU cycles to the idle domain(?)
regardless of the scheduling policy.

> I do not see this in i386 with BVT.

So maybe it assumes that the guest kernels run in ring1.

> [root@e326-1 src]# xm dmesg | grep sched
> (XEN) Using scheduler: Borrowed Virtual Time (bvt)
> [root@e326-1 src]# xm dmesg | grep -i changeset
>  Latest ChangeSet: Tue Jul 12 08:19:10 2005
> 9f6057761c8f485b1948fdd3308ae10e3ea66ad5
> -Andrew

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