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[Xen-devel] RE: Xen performance and Dbench

To: "Anthony Liguori" <anthony@xxxxxxxxxxxxx>, "deshantm@xxxxxxxxx" <deshantm@xxxxxxxxx>
Subject: [Xen-devel] RE: Xen performance and Dbench
From: "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>
Date: Thu, 7 Aug 2008 16:23:25 -0600
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Thanks, Anthony, very illuminating.  However one would
expect that the 1-cpu measurement would be about one-half
of the 2-cpu measurement, not closer to one-fourth (27%),
true?  So even if the methodology is bad, the results
may still be indicating something wrong that should
be looked at?

Todd, the references you provide are several years and
several versions of Xen old.  Have you seen any Xen
dbench results on a more recent Xen version?  While
I agree that dbench might not be the best benchmark
in the world, if some customers use and believe it
(or, worse, believe the OLS paper), it would be nice
to be able to set the record straight.

> -----Original Message-----
> From: Anthony Liguori [mailto:anthony@xxxxxxxxxxxxx]
> Sent: Thursday, August 07, 2008 1:50 PM
> To: deshantm@xxxxxxxxx
> Cc: dan.magenheimer@xxxxxxxxxx; Xen-Devel (E-mail)
> Subject: Re: Xen performance and Dbench
> Todd Deshane wrote:
> > dbench is an interesting test since it is basically an I/O 
> test (Samba test)
> > http://samba.org/ftp/tridge/dbench/README
> dbench is actually *not* an I/O test.  It mostly stresses a 
> filesystems
> interaction with the page cache.  It's heavily threaded and tends to
> scale okay but it's rarely impacted heavily by the underlying storage
> systems I/O performance.  It tends to demonstrate shadow page 
> table SMP
> scalability more than I/O performance.
> The OLS paper referenced really had bad methodologies.  If you read
> carefully, their host system was a 2-way system.  They ran all of the
> guests UP though.  Since they didn't do a parallel make, it 
> wasn't very
> obvious for their "kernel build" but it became obvious with 
> dbench since
> there were multiple threads.
> So native and "VServer" had access to both CPU cores whereas Xen, KVM,
> et al were only running on a single core.  There's no way 
> dbench is 30%
> of native under Xen.  That should have been a big red flag that
> something was wrong.
> Regards,
> Anthony Liguori
> > I don't know if dbench is the best test to determine if Xen 
> (or other
> > virts) need
> > to be fixed.
> >
> > Cheers,
> > Todd
> >
> >
> >> ===================================
> >> Thanks... for the memory
> >> I really could use more / My throughput's on the floor
> >> The balloon is flat / My swap disk's fat / I've OOM's in store
> >> Overcommitted so much
> >> (with apologies to the late great Bob Hope)
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-devel
> >>
> >>
> >
> >
> >

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