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RE: [Xen-devel] New MPI benchmark performance results (update)

  • To: "xuehai zhang" <hai@xxxxxxxxxxxxxxx>, <Xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
  • Date: Tue, 3 May 2005 14:56:38 +0100
  • Delivery-date: Tue, 03 May 2005 13:56:22 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcVPwCjADfJg+871Tty4b8cj6I39TwAJykCw
  • Thread-topic: [Xen-devel] New MPI benchmark performance results (update)

> In the graphs presented on the webpage, we take the results 
> of native Linux as the reference and normalize the other 3 
> scenarios to it. We observe a general pattern that usually 
> dom0 has a better performance than domU with SMP than domU 
> without SMP (here better performance means low latency and 
> high throughput). However, we also notice very big 
> performance gap between domU (w/o SMP) and native linux (or 
> dom0 because generally dom0 has a very similar performance as 
> native linux). Some distinct examples are: 8-node SendRecv 
> latency (max domU/linux score ~ 18), 8-node Allgather latency 
> (max domU/linux score ~ 17), and 8-node Alltoall latency (max 
> domU/linux > 60). The performance difference in the last 
> example is HUGE and we could not think about a reasonable 
> explaination why transferring 512B message size is so much 
> different than other sizes. We appreciate if you can provide 
> your insight to such a big performance problem in these benchmarks.

I still don't quite understand your experimental setup. What version of
Xen are you using? How many CPUs does each node have? How many domU's do
you run on a single node?

As regards the anomalous result for 512B AlltoAll performance, the best
way to track this down would be to use xen-oprofile. Is it reliably
repeatable? Really bad results are usually due to packets being dropped
somewhere -- there hasn't ben a whole lot of effort put into UDP
performance because so few applications use it.



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