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

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> 
> 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.

Ian


 

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