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

Matthew Palmer
Mon, 05 Jun 2006 03:53:20 -0000

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"