Overclocking PLINQ

Today I finally got around to tweaking my new PCs settings to achieve a small CPU overclock. I have an Intel Core i7 920, that by default runs at 2.66 Ghz, it’s now running at just over 3.00 Ghz, what’s this got to do with .NET you ask?

Well I thought I would post a simple follow up to my Sep 2009 entry about PLINQ and the Stack Overflow data-dump where at the time I was using a Core 2 Duo at 2.53 Ghz to run PLINQ vs LINQ speed-up tests.

So before the Core i7 speed up took place I ran the PLINQ queries and took down the results, now after the overclock I have some even more improved times.

Note: The standard LINQ queries also take advantage of a faster CPU even when using only a single core.

As an up front summary the speed-up on the PLINQ query over the LINQ query for the 4 physical cores on the Core i7 is averaging out to 3.79 factor speed-up.

This is a great value, since it’s reasonably close to 4, with some overheads not letting it reach any closer to 4. The overheads obviously prevent us from obtaining a pure number-of-cores performance multiplier.

The key experiment of data processing I’m performing here is on approximately 265,000 rows of Stack Overflow question data. After being extracted out and stored in memory some kind of data manipulation is being run (one that ideally can benefit from being distributed across several cores). Referring back to the original post it’s really just a trivial calculation of number of tags on the question that are also listed in the question body text.

So I ran LINQ then the PLINQ queries on the approximately 265,000 rows of data and averaged the results. Mind you the results are fairly consistent, almost always under 500 millisecond variations. I quickly whipped up an Excel chart to visual sumarise the time taken to complete the LINQ and PLINQ queries.

Core i7 PLINQ Timings

Core i7 PLINQ Timings (times are in Seconds)

To summarise; what was already known before we began (based on my dual core tests in September 2009)

  • More cores = better PLINQ execution time.
  • And higher core speed = better execution time.
  • Combining the two is even better.

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