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Sockets vs. MPI

August 16, 2010 at 12:00 pm PST

I briefly mentioned in a prior blog entry that I’m on a panel at the Hot Interconnects conference this Wednesday evening entitled, “Stuck with Sockets: Why is the network programming interface still from the 1980s?“.

The topic is an interesting one: sockets are, by far, the dominant user-level networking abstraction.  Countless millions (billions?) of lines of code exist that use various forms and features of the BSD sockets API (there are other sockets APIs, but let’s limit the discussion here to just the BSD API for the sake of brevity).  But networking hardware (and software!) has advanced significantly since the sockets API was introduced.  Several attempts have been made to advance the state of the art of the sockets API — to include replacing it with something else — but none have succeeded.  Why?  Is the inertia of existing sockets code too resistant to any change?

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int MPI_Vacation(short duration);

August 13, 2010 at 12:00 pm PST

The little-known “vacation” MPI function allows one to suspend the calling MPI process for brief periods of time.  The return value is an array of events that were missed while the process was inactive.  Note that the “duration” parameter is constrained to be a short value.

Programmers should also note that the returned array size tends to be large (typically regardless of the duration parameter value).  Care should be taken to ensure that enough resources are dedicated to to processing the pending events while also responding to new events in a timely manner.

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Why do different MPI’s perform differently?

July 31, 2010 at 12:00 pm PST

Sometimes my wife wonders why I have a job.  She asks me: “Aren’t you just moving bytes from point A to point B?  How hard is that?”

In some ways, she’s right — it’s not hard. Any computer users effects the act of moving bytes from point A to point B oodles of times a day.  Email, for example, is message passing — the heart of email is moving bytes from point A to point B.

But like most real-world engineering issues, it’s not quite that simple.  Indeed, if you talk to most email server administrators, they will readily launch into highly complex discussions of how delivering an email from point A to point B is an incredibly intricate, complicated process.

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Hot Interconnects evening panel

July 23, 2010 at 12:00 pm PST

The program has finally been published: I’m looking forward to being on the evening panel at the 18th Hot Interconnects conference in August.  The one-line topic for the panel is:

Stuck with Sockets: Why is the network programming interface still from the 1980s?

I’m told that it’s a good panel — a fun panel.  A panel that is deeply technical, highly opinionated, and fairly provacitive.  At least, I’m told that that’s how it’s been at the last few HOTI conferences. 

 

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MPI spice

July 20, 2010 at 12:00 pm PST

Hello programmers.  Look at your code.  Now look at MPI.  Now back at your code.  Now back to MPI

Sadly, your code isn’t parallel.  But if it stopped using global variables, it could act like MPI. 

Look down.  Back up.  Where are you?  On a 64-node, 32-core parallel computation cluster, with the code your code could act like. 

What’s in your hand?  Back at me.  I have it.  It’s an iPhone with an app for that thing you love. 

Look again.  The app is now a fully-parallelized, highly-scalable MPI code.

Anything is possible when your code acts like MPI and not like Cobol.

I’m on a horse.

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