[Beowulf] Again about NUMA (numactl and taskset)

Mikhail Kuzminsky kus at free.net
Wed Jun 25 12:34:53 EDT 2008

Let me assume now the following situation. I have OpenMP-parallelized 
application which have the number of processes equal to number of CPU 
cores per server. And let me assume that this application uses not too 
more virtual memory, so all the real memory used may be placed in RAM 
of *one* node. 

It's not the abstract question - a lot of Gaussian-03 jobs we have fit 
to this situation, and all the 8 cores for dual socket quad core 
Opteron server will be "well loaded".

Is it right that all the application memory (w/o using of numactl) 
will be allocated (by Linux kernel) in *one* node ? Then only one 
memory controller will be used. 

OK, then if I have the same server but w/2 times more small memory 
size (it's enough for run of this Gaussian-03 job !) and DIMMs are 
populating both nodes, then the performance of this server will be 
higher ! - because both memory controllers (and therefore more memory 
channels) will work simultaneously.

Is it right - that more cheap server will have higher performance for 
like cases ??

Mikhail Kuzminsky
Computer Assistance to Chemical Research Center
Zelinsky Institute of Organic Chemistry
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