Slow 4930K

[gbozo]

I have a new Core i7 - 4930K hexa-core computer whose performance is very disappointing. I'm running it in a cluster of 3 computers, the others being Core i7 quad cores (4770 and 3770K). All are running Ubuntu 12.04 and OpenMPI. With 12 MPI processes on the 4930K and 8 MPI processes on each of the quad cores, the 4930K consistently runs a factor of 2.5 slower than the quads. That is, each process on the 4930K takes 2.5 times longer to complete a lengthy cpu-bound task. (90 minutes versus 35 minutes). The 4930K is on the ASUS Sabertooth motherboard. I've tried various tuning options provided in the ASUS bios with little effect. Any ideas?

 

[Ultima99]

Sounds like you should try a cpu benchmark with known expected results. Sandra, Prime, etc

 

[gbozo]

I think the problem is that the Core i7 systems are highly susceptable to memory contention. I didn't realize it until now, but my recent tests indicate that the 3770K has the same problem, although perhaps not quite as bad. As more threads are utilized, the performance per thread decreases significantly. I found something by Eadline that illustrates this more generally (not necessarily for the Core i7s): http://www.sicorp.com/blogs/75-evaluating-multi-core-for-hpc.html . The Core i7s may not be the right machines for HPC.