Re: [Xen-users] Test - how many XEN VPS can run on my server

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Mon, May 24, 2010 at 3:12 PM, Shvayakov A. <a.shvayakov@xxxxxxxxx> wrote:
> I hope to calculate the critical number of UPU and was looking for a
> point nonlinear parameter changes, but I get unstable situation
>
> Sometime I get:
> BUG: soft lockup - CPU#1 stuck for 61s! [sshd:769]
> BUG: soft lockup - CPU#8 stuck for 61s! [swapper:0]
>
> Kernel parameter kernel.softlockup_thresh = 60 and unavailable for
> change.

linux-image-2.6.26-2-xen-amd64 is known to have some problems, and
this might be one of them. I'm not sure if Debian guys even maintain
it anymore.

If it were me, I'd go with known-to-work configuration with
well-maintained kernel. Centos 5.4/RHEL 5.5 is a good start. Since
you're basically only use apache and rsync, it should be sufficient
for your test.

Another option would be to try newer kernels and hope the problem was
fixed there. This might be a little hard though, and does not
guarantee to fix your problem.

>> I'd start by looking at disk statistics. It's possible that you're
>> running out of disk IOPS. Try "iostat -x 3" on dom0, and see if disk
>> utilization is at 100%.
>
> Yes - ioutil% is growing very rapidly and without any apparent reason

Why did you say "without any apparent reason"? AFAIK by default every
reads to a file will result in a write to update atime. That's why I
usually set mount option "noatime". Your test should be I/O heavy. In
that case the bottleneck would be your disk, not CPU or memory. Having
lots of properly-configured disk might help. If the disk is only 4 x 1
TB (for example), then you definitely need to increase the number of
disks to support that many I/O-intensive domUs.

-- 
Fajar

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