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[Xen-devel] Re: Xen performance and Dbench

To: deshantm@xxxxxxxxx
Subject: [Xen-devel] Re: Xen performance and Dbench
From: Anthony Liguori <anthony@xxxxxxxxxxxxx>
Date: Thu, 07 Aug 2008 14:49:50 -0500
Cc: "dan.magenheimer@xxxxxxxxxx" <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Todd Deshane wrote:
dbench is an interesting test since it is basically an I/O test (Samba test)

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.


Anthony Liguori

I don't know if dbench is the best test to determine if Xen (or other
virts) need
to be fixed.


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)
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