[Haskell-cafe] GC times with +RTS -N2 -s

When I run the sudoko2 program from the parconc-examples package, I get output like: ... SPARKS: 2 (1 converted, 0 overflowed, 0 dud, 0 GC'd, 1 fizzled) INIT time 0.00s ( 0.02s elapsed) MUT time 1.75s ( 1.44s elapsed) GC time 0.73s ( 0.14s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 2.48s ( 1.60s elapsed) ... My full command line is: ./sudoku2 sudoku17.1000.txt +RTS -N2 -s I understand how to interpret the Total time - 2.48 seconds is the total time spent by both cores and 1.6 seconds is the running time of the program as a whole. But how should interpret the GC times? What do 0.73s and 0.14s actually represent? This is with GHC 7.8.3, OSX 10.8.5, 64-bit Haskell Platform.