Is there such a thing as too many threads?  Of course there is.  Well, for the time being, that is.

I am currently putting together an audio conversion application, and I was doing some testing to see what number of concurrent conversions produced the best results in respect to time.  Conventional wisdom says that “bigger/more is better”, but not necessarily in this case.

During my testing, I converted a series of 15 songs from FLAC format to AAC format, all on the same PC armed with a 3.0 GHz Quad Core processor and 4 GB of memory.  The drive on which the data was stored and written to is a Seagate Barracuda SATA drive.  I simply ran the conversion using one thread and incremented the thread count after each iteration until I had 8 concurrent threads running.

The results are as follows:

1 Thread – 125 Seconds
2 Threads – 64 Seconds (-61s)
3 Threads – 45 Seconds (-19s)
4 Threads – 36 Seconds (-9s)
5 Threads – 37 Seconds (+1s)
6 Threads – 35 Seconds (-2s)
7 Threads – 35 Seconds (-0s)
8 Threads – 35 Seconds (-0s)

As you can see, performance pretty much plateaus around the 4 Thread mark and barely increases after that.

It makes sense that a 4-core machine gets good performance when 4 separate threads are running.  The processor was not being utilized 100% however, which is why I decided to try increasing the concurrent thread count.

I would assume that the extra overhead involved with managing additional threads, along with the cost of constant context-switching at the core-level outweighs the benefits of having additional processes running at the same time.  Initially, I thought that the hard drive might be the limiting factor here, but when running the same conversion from two SATA drives in RAID 0 configuration, the results were almost identical.  Using memory streams instead of the hard drives for temporary file storage also had little effect (+/- 1 second) on the results.

So there you have it, more threads is not necessarily always better.  I really could have told you that before I tried this little experiment, but I liked the process of producing tangible results showing that this is the case.

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