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Process affinity: Hop on the bus, Gus!

January 10, 2014 at 5:00 am PST

Today’s blog post is written by Joshua Ladd, Open MPI developer and HPC Algorithms Engineer at Mellanox Technologies.

At some point in the process of pondering this blog post I noticed that my subconscious had, much to my annoyance, registered a snippet of the chorus to Paul Simon’s timeless classic “50 Ways to Leave Your Lover” with my brain’s internal progress thread. Seemingly, endlessly repeating, billions of times over (well, at least ten times over) the catchy hook that offers one, of presumably 50, possible ways to leave one’s lover -- “Hop on the bus, Gus.” Assuming Gus does indeed wish to extricate himself from a passionate predicament, this seems a reasonable suggestion. But, supposing Gus has a really jilted lover; his response to Mr. Simon’s exhortation might be “Just how many hops to that damn bus, Paul?”

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EuroMPI’13 Cisco slides: Open MPI Process Affinity User Interface

September 18, 2013 at 5:17 am PST

The slides below are from my presentation at EuroMPI’13 about Open MPI’s flexible process affinity interface (in OMPI 1.7.2 and later).  I described this system in a prior blog entries (one, two, three), but many people keep asking me about it.

Josh Hursey from U. Wisconsin, LaCrosse, wrote this IMUDI paper about the interface (IMUDI is a sub-workshop of EuroMPI focusing on end-user issues) to get a little more publicity and awareness of this process affinity system.  Specifically, we designed this affinity system so that we could get feedback from real end users about what is useful and what is not.

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How many network links do you have for MPI traffic?

July 19, 2013 at 5:00 am PST

If you’re a bargain basement HPC user, you might well scoff at the idea of having more than one network interface for your MPI traffic.

“I’ve got (insert your favorite high bandwidth network name here)! That’s plenty to serve all my cores! Why would I need more than that?”

I can think of (at least) three reasons off the top of my head.

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Process and memory affinity: why do you care?

January 31, 2013 at 5:00 am PST

I’ve written about NUMA effects and process affinity on this blog lots of times in the past.  It’s a complex topic that has a lot of real-world affects on your MPI and HPC applications.  If you’re not using processor and memory affinity, you’re likely experiencing performance degradation without even realizing it.

In short:

  1. If you’re not booting your Linux kernel in NUMA mode, you should be.
  2. If you’re not using processor affinity with your MPI/HPC applications, you should be.

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Process Affinity in OMPI v1.7 (part 2)

September 11, 2012 at 5:00 am PST

In my last post, I described the Simple mode of Open MPI v1.7′s process affinity system.

The Simple mode is actually quite flexible, and we anticipate that it will meet most users’ needs. However, some users will need more flexibility. That’s what the Expert mode is for.

Before jumping in to the Expert mode, though, let me describe two more features of the revamped v1.7 affinity system.

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