[mpich-discuss] mpich-discuss Digest, Vol 14, Issue 37

[Darius Buntinas]

We have noticed performance issues as well on certain machines, but we
haven't pinned the cause down yet.

BTW, process-core binding is very important for getting consistent
performance measurements, especially for intranode communication.
You'll get the best performance when the processes share an L2 cache.

Here's a page with hints on how to get the best benchmark performance
from mpich2:
http://wiki.mcs.anl.gov/mpich2/index.php/Measuring_Nemesis_Performance

Can you send us the output of the following commands on the machine
you're running the benchmarks on to help us debug the performance
problem you're seeing?

ls /sys/devices/system/cpu/cpu*/cache/index*/shared_cpu_map
cat /sys/devices/system/cpu/cpu*/cache/index*/shared_cpu_map
cat /sys/devices/system/cpu/cpu*/cache/index*/size

Thanks
-d



On 11/24/2009 03:08 AM, BryantMichael Bryant wrote:
> hello,recently i had do a research about mpich2 to compare the
> "nemesis" and "shm" channel.in the research,first, i make install mpich2
> with nemesis,and then make install with shm. my purpose is to compare
> the latency and bandwidth by using the two channel in a single SMP node.
> the test enviroment is Intel(R) Xeon(R) CPU X5355 2.66GH,cache size :
> 4096 KB
> and  the test result shows that the bandwidth,when the mpi message size
> from 1-32Byte,the bandwidth shows similar;then the message size from
> 32-512B,the nemesis shows little better than shm;but after 512B to
> 1MB(my test use OSU benchmark,message size from 1Byte-4MB),the shm show
> more better than the nemesis,the peak is about 1800MBps(shm),but the
> nemesis is only 1100MBps;from 1MB to 4MB,the bandwidth in shm decrease
> rapidly,anyway it also better than the nemesis,when the message size
> come to 4MB,the nemesis and shm show the similar bandwidth.
> my question is: why the shm show the more better performance than the
> nemesis? is it owing to the data transfer method or shm has some
> optimize functions ?
> pls tell me ,thank you!
> 
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