#8231: Haskell's Run Time System doesn't save electricity --------------------------+------------------------------------------------ Reporter: | Owner: UnixJunkie | Status: new Type: bug | Milestone: Priority: normal | Version: 7.4.1 Component: | Operating System: Linux Runtime System | Type of failure: None/Unknown Keywords: energy | Test Case: provided in the description saving | Blocking: Architecture: x86_64 | (amd64) | Difficulty: | Unknown | Blocked By: | Related Tickets: | --------------------------+------------------------------------------------ Someone provided me with a sequential implementation of the fibonacci function. Out of curiosity, it was compiled with -threaded and we played with the -N option of the runtime. That same someone noticed some suspicious behavior. I notice the same and so report about it: all cores specified by $np are fully used while there is no change in the wallclock time spent by the program. The code: --- {{{ import Text.Printf fib :: Int -> Int fib 0 = 0 fib 1 = 1 fib n = fib (n - 1) + fib (n - 2) i = 44 main = printf "n=%d => %d\n" i (fib i) }}} --- The build: --- {{{ ghc -threaded -O2 sequential_fib.hs }}} --- The run (on an eight cores machine), shell is Bash: --- {{{ for np in `seq 1 8` ; do time ./sequential_fib +RTS -N$np ; done }}} --- The output: --- {{{ n=44 => 701408733 real 0m10.838s user 0m10.817s sys 0m0.000s n=44 => 701408733 real 0m10.762s user 0m12.009s sys 0m9.165s n=44 => 701408733 real 0m10.774s user 0m24.846s sys 0m6.800s n=44 => 701408733 real 0m10.769s user 0m33.654s sys 0m8.413s n=44 => 701408733 real 0m11.222s user 0m47.427s sys 0m7.336s n=44 => 701408733 real 0m11.217s user 0m57.872s sys 0m7.752s n=44 => 701408733 real 0m11.208s user 1m9.172s sys 0m7.112s n=44 => 701408733 real 0m11.204s user 1m18.909s sys 0m7.768s }}} --- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8231 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler