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* Massive scalability improvements to the I/O manager

Just a brief note from the front lines - I recompiled a heavily threaded program with (a recent pre-release) of 7.8.1 and got a 10% performance increase over 7.6.3. Nothing like free lunches - so thanks again for the great work!

Did you run you program on a multicore system? If so, did you specify +RTS -N<x> option? If your program uses MVar heavily, you need to re-design your program. For more information, please read: http://www.yesodweb.com/blog/2014/01/new-fast-logger --Kazu