Mailing List Archive: Xen: Users

Severe dom0 performance issues after installing Xen

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buck.alex at gmail

Sep 3, 2012, 5:38 PM

Post #1 of 4 (237 views)
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Severe dom0 performance issues after installing Xen

Hello,

I'm experiencing some severe performance issues running Xen 4.0.1 with a
cleanly-installed Debian 6 dom0. Prior to installation, the machine's
performance was fine, but after installation booting takes anywhere from
5 to 20 times longer, processes take a long time to start, and SSH
lags. No domUs are running (or have been created yet). I can switch
back to running without Xen (but still using the Xen-compatible kernel)
and the performance problems disappear.

I attempted to dig into the issue further, but haven't been able to find
any reason why the machine is so slow. Some cursory CPU integer
performance and memory bandwidth benchmarks I ran showed that there is
almost no difference in performance, and disk only loses about 10% of
its performance. I also haven't found anything particularly alarming in
dmesg or xm dmesg (although this is my first time installing Xen, so I
am not sure I would know what to look for). top and xm top don't show
anything constantly consuming all of the system's resources, and the
only additional service I've installed so far is ntpd. As an additional
debugging step, I've attempted limiting the dom0 memory to 1536MB (the
machine has 4GB of physical memory). I haven't managed to turn up
anything about this on Google yet.

Has anyone seen a similar issue before or have ideas on how to fix/debug
it? I have no physical access to the machine, unfortunately, so I am
unable to play with BIOS settings. I've attached the contents of dmesg
and xm dmesg, should these be useful.

Thanks,
Keith

Attachments:

dmesg (59.2 KB)

xm-dmesg (4.17 KB)

raju at linux-delhi

Sep 3, 2012, 7:00 PM

Post #2 of 4 (215 views)
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Re: Severe dom0 performance issues after installing Xen [In reply to]

On Tuesday 04 Sep 2012, Keith Buck wrote:
> I'm experiencing some severe performance issues running Xen 4.0.1
> with a cleanly-installed Debian 6 dom0. Prior to installation, the
> machine's performance was fine, but after installation booting takes
> anywhere from 5 to 20 times longer, processes take a long time to
> start, and SSH lags. No domUs are running (or have been created
> yet). I can switch back to running without Xen (but still using the
> Xen-compatible kernel) and the performance problems disappear.

Probably a stupid question, but sometime we miss the obvious: did you
make any networking changes? Specifically, could this problem be due to
not being able to reverse resolve IP addresses on your machine?

Regards,

-- Raj
--
Raj Mathur || raju [at] kandalaya || GPG:
http://otheronepercent.blogspot.com || http://kandalaya.org || CC68
It is the mind that moves || http://schizoid.in || D17F

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buck.alex at gmail

Sep 3, 2012, 7:16 PM

Post #3 of 4 (216 views)
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Re: Severe dom0 performance issues after installing Xen [In reply to]

On Mon, Sep 3, 2012 at 7:00 PM, Raj Mathur (राज माथुर) <raju [at] linux-delhi
> wrote:

> On Tuesday 04 Sep 2012, Keith Buck wrote:
> > I'm experiencing some severe performance issues running Xen 4.0.1
> > with a cleanly-installed Debian 6 dom0. Prior to installation, the
> > machine's performance was fine, but after installation booting takes
> > anywhere from 5 to 20 times longer, processes take a long time to
> > start, and SSH lags. No domUs are running (or have been created
> > yet). I can switch back to running without Xen (but still using the
> > Xen-compatible kernel) and the performance problems disappear.
>
> Probably a stupid question, but sometime we miss the obvious: did you
> make any networking changes? Specifically, could this problem be due to
> not being able to reverse resolve IP addresses on your machine?
>
> I haven't made any networking changes. The SSH latency isn't just logging
in, there's also latency echoing back what I type at the prompt and
displaying the output of programs.

nd at syndicat

Sep 3, 2012, 10:43 PM

Post #4 of 4 (216 views)
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Re: Severe dom0 performance issues after installing Xen [In reply to]

...not shure what's going on there, but would try following things:

- try to boot with kernel options noapic
- try to pin one CPU directly to Dom0 and set max cpu to 1 on Dom0 (xen and kernel options)
- try to boot with disabled acpi etc.
- try to find out "what" is slow, i.e. I/O, CPU, net etc and what not

Is there any "point" to recognize during boot when the system "got slow"?

Best regards,

Niels.

"Raj Mathur (राज माथुर)" <raju [at] linux-delhi> schrieb:

>On Tuesday 04 Sep 2012, Keith Buck wrote:
>> I'm experiencing some severe performance issues running Xen 4.0.1
>> with a cleanly-installed Debian 6 dom0. Prior to installation, the
>> machine's performance was fine, but after installation booting takes
>> anywhere from 5 to 20 times longer, processes take a long time to
>> start, and SSH lags. No domUs are running (or have been created
>> yet). I can switch back to running without Xen (but still using the
>> Xen-compatible kernel) and the performance problems disappear.
>
>Probably a stupid question, but sometime we miss the obvious: did you
>make any networking changes? Specifically, could this problem be due
>to
>not being able to reverse resolve IP addresses on your machine?
>
>Regards,
>
>-- Raj
>--
>Raj Mathur || raju [at] kandalaya || GPG:
>http://otheronepercent.blogspot.com || http://kandalaya.org || CC68
>It is the mind that moves || http://schizoid.in || D17F
>
>____________________________________________

--
Niels Dettenbach
Syndicat IT&Internet
http://www.syndicat.com

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