[Xen-users] Re: Java non-performant in a domU?

[Matthew Palmer <mpalmer@xxxxxxxxxxx>]

On Sun, Jun 04, 2006 at 10:08:58PM -0500, Christopher G. Stach II wrote:
> Matthew Palmer wrote:
> > Has anyone else seen a significant reduction in performance of Java
> > applications running in a domU?  We're seeing a reduction in performance of
> > around 30% when running a Java (Tomcat, etc webapp) in a domU over running
> > it natively -- this is significantly worse than what we see for other
> > applications.
> > 
> > Wondering if anyone else has seen this problem (so we know we're not going
> > nuts), and whether you were able to tune things to make it perform
> > acceptably.
> 
> I run lots of Sun JVMs (1.4.2 and 1.5.0 running Tomcat 5.0, Eclipse
> 3.1.2 and 3.2, Resin 3.0.14) in VMs and they perform about as well as
> expected, being that the machine is being used by other VMs and Xen has
> a little overhead.  They're certainly not as fast as they normally are,
> but not 30% slower when nothing else is loading the machine.
> 
> Is it memory, disk, or CPU that isn't performing as well?

That's the crazy thing -- we've been monitoring everything we can, and we
can't find any anomalous bottlenecks.  The application is naturally CPU
bound, and we're giving it the same amount of resources it normally gets --
plenty of RAM (never touches swap), all of the system CPUs, and the machine
is doing *nothing* else while we're benchmarking.  It's pegging on the CPUs,
running at a nice healthy 350% of CPU (as per xentop, on a 4-way machine),
and there isn't a lot of disk I/O, but we're only seeing 100 transactions
per second (against a baseline of 140 transactions per second on a fully
native machine).

We're running AMD64 systems, and we've tried with a 64-bit domU userland
with a 32-bit JVM (the app doesn't run in a 64-bin JVM, because of 3rd party
libraries that are running -- so much for platform undependence...), and a
32-bit domU userland over the 64-bit kernel.  For the 32-bit userland, we've
used a Xen-friendly patched glibc, to give us TLS without having to emulate
segment stuff.

Perhaps that's it -- we need to run a full 32-bit OS (including the kernel)
on these AMD64 boxes, and Xen on top of that.

- Matt

-- 
<liw> hut.fi has or used to have two nfs servers not-responding and
still-trying... don't know if their dns server was not-found... 4o4 would be
then a good name for the web server... endless hours of fun
<aj> "did you get a response from 4o4?" "nah, it just 404ed"

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