Re: [Xen-devel] Performance issuses with Splash2 applications on XEN

["Mark A. Williamson" <mark.williamson@xxxxxxxxxxxx>]

> domU (1GB RAM) is booted from a file-backed VBD on a local HDD (I have
> tested this on a LVM-backed VBD over NFS and see no significant
> differences).

I wouldn't recommend exporting filesystems that require high performance over 
NFS either.  Is there any reason not to export the LVM volume directly?  i.e.

disk = [ 'phy:/path/to/lvm/volume,sda1,w']

This is the preferred configuration for doing serious amounts of IO, since 
either loop files or NFS will add a load of overhead.

Cheers,
Mark

>
> The splash applications that I am using, use the lpthread library. So when
> I refer to running an application with multiple processors, I am referring
> to multiple threads <this is how they call it>.
>
> The splash applications use a LOT of synchronization objects during their
> operation (e.g., mutex and conditional variables). Other than that, they
> simply allocate memory and do a lot of mathematical computations (I.e.,
> floating point).
>
> Could the pthread library operations (I.e., pthread synchronization
> objects) be the cause of the performance hit within domain?
>
>
>
> Hardware:
>
> Tyan s2882 Motherboard
>
> Dual 2.0 Ghz AMD Opteron
>
> 2GB of RAM
>
> Broadcom GB NIC
>
>
>
>
>
>
>
> Jessie Smart
>
> jessiesmart354@xxxxxxxxx <mailto:jessiesmart354@xxxxxxxxx>
>
>
> Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx> wrote:
> Is this using SMP guests from the unstable tree? If so, there's some
> serious scheduler issues which are currently being worked on -- its
> certainly not ready for serious benchmarking (though this might be
> useful application for us to use for tuning purposes).
>
> How many CPUs has the machine you're running on? How many virtual CPUS
> does the guest have?
>
> Ian
>
> > -----Original Message-----
> > From: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx
> > [mailto:xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of
> > jessie smart
> > Sent: 02 February 2005 20:23
> > To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
> > Subject: [Xen-devel] Performance issuses with Splash2
> > applications on XEN
> >
> > I am running one of the applications from the Stanford
> > splash2 application suite (
> > http://www-flash.stanford.edu/apps/ ) and getting an
> > unexpected (~5x) performance decrease in domU when specifying
> > more than 1 processor in the application. dom0 seems to
> > handle this fine.
> >
> >
> >
> > Specificly I am seeing this on the water-nsquared app. I am
> > not going to give my machine config here (if you need them
> > please ask) just the differences in runtime and the
> > parameters of the app.
> >
> >
> >
> >
> >
> > all are running single processor & 1GB RAM
> >
> > (times reported as real/user/system, in seconds)
> >
> >
> >
> > water-nsquared 64 processors 8000 molecules
> >
> >
> >
> > baseline (non-xen) 72.20/78.80/0.17
> >
> > Dom0 77.76/77.17/0.16
> >
> > DomU 357.24/357.04/0.018
> >
> >
> >
> > water-nsquared 1 processor 8000 molecules
> >
> >
> >
> > baseline (non-xen) 73.16/72.75/0.15
> >
> > Dom0 72.75/72.37/0.02
> >
> > DomU 66.07/66.04/0.02
> >
> >
> >
> >
> >
> > I have disabled the /lib/tls.
> >
> >
> >
> > I am hoping that someone here with a little more experience
> > with Xen can help me try to explain this. Any input would be
> > greatly appreciated.
> >
> >
> >
> > Jessie
> >
> > jessiesmart354@xxxxxxxxx
> >
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