Thank you! Now it's rather clear for me.
Mon, 4 Aug 2014 06:47:34 +0100 от Matthew Flatt <mfl...@cs.utah.edu>: >Well... a function call is expensive relative to some things, such as >adding fixnums to produce a fixnum. > > >My read of your initial results is that calling an unknown function is >similar to the cost of one iteration in a loop that sets a character in >a string. > >More precisely, decompiling the program shows that the compiler unrolls >the loop in `test1` by 4 iterations, so one call to an unknown function >is the same cost as 4 generic `<`s on fixnums, 4 generic `+ 1`s on >fixnums, 4 `integer->char`s, 4 `string-set!s`, and one jump to a known >function (to recur). > >The `build-string1` loop is similarly unrolled 4 times, and the call to >`build-string1` is not inlined in `test3`, so we really can compare the >unknown function call in `test3` to the overall loop overhead plus >`string-set!`s of `test1`. And the fact that neither `build-string1` >nor `test2 is inlined is consistent with `test2` and `test3` having the >same performance. > >If I change the `for` body of `test1` with a constant, then the time is >cut in half. So, a `string-set!` takes up about half of the time. > > >Putting that all together, it looks like a call to an unknown function >takes about twice the time of a `string-set!` --- which (due to various >tag and bounds checks for the string assignment) costs the same as a >small pile of generic arithmetic on fixnums. That could be considered >expensive in a tight loop. > >I would hesitate to say that higher order functions are always slow, >because many uses do more work around the call than set one character >in a string. > > >At Mon, 04 Aug 2014 07:42:53 +0400, Roman Klochkov wrote: >> > unknown function call is expensive >> >> So, higher order function always slow. >> Thus, to improve performance, one should use for/fold, for/list, ... and >> never >> use map, foldl, build-string, ... with lambda. >> Is it correct? >> >> Sun, 3 Aug 2014 13:15:57 -0400 от Matthias Felleisen < matth...@ccs.neu.edu >> >: >> > >> >Because build-string calls an unknown function 1000 x 100000 times, and an >> unknown function call is expensive. >> > >> >Racket could possible collapse all modules and perform additional in-lining >> optimizations eventually, which may help here. But it doesn't yet. >> > >> >-- Matthias >> > >> > >> > >> >On Aug 3, 2014, at 5:15 AM, Roman Klochkov wrote: >> >>Are higher order function always slow? >> >>... >> >>--- >> >> >> >>So I see, that build-string version is about two times slower, than >> set-in-the-loop. Why so much? I expected about 10-20% difference. >> >>-- >> >>Roman Klochkov ____________________ >> >> Racket Users list: >> >> http://lists.racket-lang.org/users >> > >> >> >> -- >> Roman Klochkov >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users -- Roman Klochkov
____________________ Racket Users list: http://lists.racket-lang.org/users
