[Haskell-cafe] GHCi timing statistics
eric at seidel.io
Thu Mar 5 22:26:31 UTC 2015
I believe `:set +s` displays cpu time, not wall-clock time.
On Thu, Mar 5, 2015, at 14:23, David Rush wrote:
> Hi all -
> Is it my imagination, or are the statistics printed by GHCi when :set +s
> has been enabled entirely spurious when SMP parallelism is turned on? I'm
> trying to determine if I am actually getting any improvement, and - both
> by the wall clock and by the reported statistics I don't seem to be;
> however, the reported statistics don't seem to line up very well with the
> wall clock time.
> An additional oddity that I've noted is that my algorithm's reference
> implementation - which simply can't run in parallel due to a foolishly
> introduced data dependency - still seems to kick 16 CPUs well into the
> 90%+ utilization range when I have +RTS -N. This code has no parallelism
> primitives in it whatsoever.
> I realize that I'm not being terribly rigorous in my description here,
> that is partly because I am not sure how to report on this yet. I think
> next step is going to be to build a standalone executable to check using
> the Unix time command.
> For reference I am running Haskell platform from Debian Jessie on a 16-
> core amd64 system with 29GiB or RAM available. This would appear to be
> 7.6.3 :(
> - d
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