Dear GHC developers, I tried to test the ghc-6.6.1 performance on long lists. And there is something a bit suspicious about the test. Consider the program ----------------------------------------- main = putStr (shows res "\n") where n = k*10^6 :: Int k = 2 -- put k = 2,4,6, ... res = head $ rev [1 .. n] rev xs = r [] xs where r xs [] = xs r xs (y: ys) = r (y: xs) ys ----------------------------------------- 512 Mb RAM machine, Pentium 4, 1.6 GHz, Debian Linux. `Making': ghc -O --make Main Running time Main +RTS -M400m -RTS ---- ghc-6.6.1 -------------------| k time [sec] minimal needed ghc-5.02.3 for 400Mb heap (-M..) [Mb] 2 1.3 41 2 sec 41 Mb 4 3.0 6 7.8 8 8.8 164 8 ------------------ 10 23.7 12 24.7 244 14 25.1 13 ----------------------------------------------------------------- Should the cost of this program be linear in k ? For example: 8/4 = 2, time(8)/time(4) = 8.8/3.0 =~= 2.9 Should this ratio be near 2.0 ? Further, at k = 10, the time jumps. This is, probably, due to that a list of 10*10^6 ints takes about 8*10*10^6 bytes =~= 80 Mb (please, is this so ?), the program may need a copy of this list ... and this total may be close to -M400M (?), and thus garbage collection happens (once). After k = 10, it looks again like linear. My impression is that at the segment k <- [2, 8] the cost is about k*(log k). Thank you in advance for your comments. Regards, ----------------- Serge Mechveliani mechvel@botik.ru