On 14/05/16 02:31 PM, Harendra Kumar wrote:
The difference seems to be entirely due to memory pressure. At list size 1000
both pure version and IO version perform equally. But as the size of the list
increases the pure version scales linearly while the IO version degrades
exponentially. Here are the execution times per list element in ns as the list
size increases:
Size of list Pure IO
1000 8.7 8.3
10000 8.7 18
100000 8.8 63
1000000 9.3 786
This seems to be due to increased GC activity in the IO case. The GC stats for
list size 1 million are:
IO case: %GC time 66.1% (61.1% elapsed)
Pure case: %GC time 2.6% (3.3% elapsed)
Not sure if there is a way to write this code in IO monad which can reduce this
overhead.
Something to be aware of is that GHC currently can't pass multiple return
values in registers (that may not be a 100% accurate statement, but a
reasonable high level summary, see ticket for details)
https://ghc.haskell.org/trac/ghc/ticket/2289
This can bite you with with the IO monad as having to pass around the world
state token turns single return values into multiple return values (i.e., the
new state token plus the returned value).
I haven't actually dug into your code to see if this is part of the problem,
but figured I would mention it.
Cheers! -Tyson
_______________________________________________
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
