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

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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