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Re: [Xen-devel] memory performance 20% degradation in DomU -- Sisu

Hi, George:

Thanks for the reply.

Yes, I have tried CPU intensive benchmark. the performance is almost the same as native case.
We also tried the same image, but on another physical host with a 3rd generation i7 processor. This time, the memory-intensive benchmark only incurs less than 5% performance degradation, and the latency is identical to native case.
We are looking into this issue now and hopefully will figure this out.

Can you be more specific about the highest performance modes of the CPU? For all the experiments, I disabled hyperthreading and frequency scaling, so CPU should work at a constant speed.


On Tue, Mar 11, 2014 at 7:03 AM, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
On Tue, Mar 4, 2014 at 11:00 PM, Sisu Xi <xisisu@xxxxxxxxx> wrote:
> Hi, all:
> I also used the ramspeed to measure memory throughput.
> http://alasir.com/software/ramspeed/
> I am using the v2.6, single core version. The command I used is ./ramspeed
> -b 3 (for int) and ./ramspeed -b 6 (for float).
> The benchmark measures four operations: add, copy, scale, and triad. And
> also gives an average number for all four operations.
> The results in DomU shows around 20% performance degradation compared to
> non-virt results.
> Attached is the results. The left part are results for int, while the right
> part is the results for float. The Y axis is the measured throughput. Each
> box contains 100 experiment repeats.
> The black boxes are the results in non-virtualized environment, while the
> blue ones are the results I got in DomU.
> The Xen version I am using is 4.3.0, 64bit.

Have you tried a CPU- but non-memory-intensive benchmark? ÂThere was
an issue some time back with the highest performance modes of the CPU
not being enabled by default, but needing special patches in either
dom0 or Xen. ÂIs it possible you're seeing something like that?


Sisu Xi, PhD Candidate

Department of Computer Science and Engineering
Campus Box 1045
Washington University in St. Louis
One Brookings Drive
St. Louis, MO 63130
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