Re: [Xen-users] VT-X on Dell Machines

[Randy Thelen <rthelen@xxxxxxxxxx>]

Adrian Wells wrote:

> is there a significant performance advantage with Xen when  
> considering 2 x 2.8 GHz Xeon dual-core CPUs vs. 2 x 3.8 GHz Xeon  
> single-core CPUs?
Depends on what you're optimizing for.  If you need single threaded  
algorithms evaluated quickly, then you want higher frequency  
processors.  If, instead, you have multiple jobs that can be  
processed simultaneously and you measure system performance by having  
them all complete faster (and in parallel), then you'd do better to  
maximize the number of cores available.
However, keep tabs on the pipeline depth of the processor you're  
choosing.  As an example of the importance of pipeline depth, a 1GHz  
Pentium III performs more work in unit time than a Pentium 4 at the  
same frequency.  (Assuming all else is equal, which it never is, see  
the next paragraph.)
Also, note the chipset.  A chipset with dual memory controllers will  
have more memory bandwidth than one with a single memory controller  
(though, typically, memory latency will remain the same).
Oh, and if you're getting into the details, you might want to  
consider the effect of a larger L2 cache on your work load.  Bigger  
is (virtually) always better.  But, bigger costs more.
Personally, the things I value when selecting a system are:

0) Amount of memory
1) # of cores
2) # of memory controllers
3) CPU architecture (fewer pipeline stages)

That's about it.  Oh, and then I maximize those given my budget.  :-)

-- Randy

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