[Haskell-cafe] A Performance Puzzle

[Claude Heiland-Allen]

Hi Gregory,

On 03/08/18 01:16, Gregory Wright wrote:
> That's an interesting point.  Could the generation of the random 
> matrix be that slow?  Something to check.
It's not that it's slow by itself, I think it's that the CAF mVals 
::[Double] is retained, taking ~40MB of heap which slows down GC.

Using criterion's `env` isn't so hard, and gets a much nicer looking 
heap profile graph.  See new benchmark code attached.

Graphs:
https://mathr.co.uk/tmp/luSolve-bench.svg
https://mathr.co.uk/tmp/luSolve-bench-env.svg

>
> On 8/2/18 7:47 PM, Vanessa McHale wrote:
>> Looking at your benchmarks you may be benchmarking the wrong thing. 
>> The function you are benchmarking is runLUFactor, which generates 
>> random matrices in addition to factoring them.
>>
>> On 08/02/2018 05:27 PM, Gregory Wright wrote:
>>> benchmarking LUSolve/luFactor 1000 x 1000 matrix
>>>
>>> time                 1.940 s    (1.685 s .. 2.139 s)
>>>                      0.998 R²   (0.993 R² .. 1.000 R²)
>>> mean                 1.826 s    (1.696 s .. 1.880 s)
>>>
I started at mean 1.50s with your code.
>>>
>>> std dev              93.63 ms   (5.802 ms .. 117.8 ms)
>>> variance introduced by outliers: 19% (moderately inflated)
>>>

Making the `env` change and compiling with -fllvm (as suggested in 
#haskell on irc.freenode.net, for a 4x speed boost) brought my time for 
that benchmark to mean 257ms. +RTS -s tells me productivity is 99.1%, 
which is pretty high.
I compiled the benchmark by hand for best speed, as cabal seems to add 
-prof which slows the bench down slightly.
I also compiled without -threaded, because the code isn't parallelized 
afaict, and parallel GC can be a bottleneck (is this still true?).


Claude
-- 
https://mathr.co.uk

-------------- next part --------------
A non-text attachment was scrubbed...
Name: LUSolveBenchmark.hs
Type: text/x-haskell
Size: 1248 bytes
Desc: not available
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20180803/48010c6f/attachment.hs>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Bench.hs
Type: text/x-haskell
Size: 213 bytes
Desc: not available
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20180803/48010c6f/attachment-0001.hs>