Re: Xen performance and Dbench

[Anthony Liguori <anthony@codemonkey.ws>]

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)
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> 
> 
>