[web-devel] Data.Word8 (word8 library)

Thu Sep 20 18:58:05 CEST 2012

On Thu, Sep 20, 2012 at 7:25 PM, Gregory Collins <greg at gregorycollins.net>wrote:

> Hey Michael,
>
> BTW -- you're getting crap performance here because of the fromEnum/toEnum
> in toLowerC, which does checks. An updated version using unsafeChr is
> faster than your bsToLower call: https://gist.github.com/3756876
>
> master /home/gdc/tmp/haskell/chr/gist-3756876 ⚠ $ ./bench
> warming up
> estimating clock resolution...
> mean is 1.290661 us (640001 iterations)
> found 2935 outliers among 639999 samples (0.5%)
>   2541 (0.4%) high severe
> estimating cost of a clock call...
> mean is 31.63774 ns (13 iterations)
> found 2 outliers among 13 samples (15.4%)
>   2 (15.4%) high mild
>
> benchmarking Char8
> mean: 145.1935 us, lb 141.4375 us, ub 149.8138 us, ci 0.950
> std dev: 21.28567 us, lb 18.14038 us, ub 23.87625 us, ci 0.950
> found 22 outliers among 100 samples (22.0%)
>   22 (22.0%) high severe
> variance introduced by outliers: 89.411%
> variance is severely inflated by outliers
>
> benchmarking Char8 toLowerC
> mean: 12.74308 us, lb 12.24657 us, ub 13.31365 us, ci 0.950
> std dev: 2.712828 us, lb 2.434402 us, ub 2.904232 us, ci 0.950
> variance introduced by outliers: 94.689%
> variance is severely inflated by outliers
>
> benchmarking bsToLower
> mean: 20.68829 us, lb 20.66869 us, ub 20.70941 us, ci 0.950
>  std dev: 104.5939 ns, lb 95.37577 ns, ub 120.6401 ns, ci 0.950
>
>
> G.
>
> On Thu, Sep 20, 2012 at 5:01 PM, Michael Snoyman <michael at snoyman.com>wrote:
>
>> Well... let's test it out:
>>
>> benchmarking Char8
>> mean: 333.0050 us, lb 329.2846 us, ub 336.2362 us, ci 0.950
>> std dev: 17.73400 us, lb 15.69876 us, ub 19.45947 us, ci 0.950
>> variance introduced by outliers: 51.452%
>> variance is severely inflated by outliers
>>
>> benchmarking Char8 toLowerC
>> mean: 117.1571 us, lb 116.8739 us, ub 117.4219 us, ci 0.950
>> std dev: 1.394150 us, lb 1.189928 us, ub 1.649276 us, ci 0.950
>>
>> benchmarking Word8
>> mean: 41.01667 us, lb 40.94708 us, ub 41.09468 us, ci 0.950
>> std dev: 378.4175 ns, lb 335.4655 ns, ub 462.6281 ns, ci 0.950
>>
>> benchmarking bsToLower
>> mean: 37.37589 us, lb 37.24453 us, ub 37.48697 us, ci 0.950
>> std dev: 616.5653 ns, lb 513.7510 ns, ub 752.8996 ns, ci 0.950
>> found 9 outliers among 100 samples (9.0%)
>>   3 (3.0%) low severe
>>   4 (4.0%) low mild
>>   2 (2.0%) high mild
>> variance introduced by outliers: 9.426%
>> variance is slightly inflated by outliers
>>
>> So a specialized `Char -> Char` function helps, but doesn't completely
>> close the performance gap. (Updates at the same gist[1].)
>>
>> I disagree with a problem with an extra package: this is such a
>> low-level detail that average users don't need to really be aware of
>> the existence of the package, and I think the marginal increase in
>> compile times shouldn't cause any issues. I used to worry much more
>> about adding extra packages to the mix, but with the more recent
>> versions of cabal-install and the community's general improvement in
>> handling dependency hell, I see less of a reason to do so.
>>
>> That said, I think having specialized toLower/toUpper in a central
>> place- perhaps even bytestring itself- would be a good thing.
>>
>> Michael
>>
>> [1] https://gist.github.com/3756212
>>
>> On Thu, Sep 20, 2012 at 5:47 PM, Gregory Collins
>> <greg at gregorycollins.net> wrote:
>> > This is, of course, not an apples-to-apples test:
>> >
>> > Prelude Data.Char> toUpper 'χ'
>> > '\935'
>> > Prelude Data.Char> putStrLn ('\935':[])
>> > Χ
>> >
>> >
>> > ...which I suppose is the point. I wonder whether a version of
>> > toUpper/toLower on Char restricted to ASCII values would have the same
>> > performance here.
>> >
>> > We only call toLower explicitly in one place in snap-server, but where
>> this
>> > would be nice to fix is for HTTP headers, where I think we are all using
>> > case-insensitive (which just calls "map toLower"). Probably we should
>> send
>> > Bas a patch to optimize the FoldCase instance for ByteString.
>> >
>> > Personally I would prefer not to have yet another tiny package here, as
>> the
>> > package zoo has enough creatures in it as it is. Do we think we have a
>> real
>> > problem here beyond the toUpper/toLower case? I suspect that for most
>> other
>> > uses of Data.ByteString.Char8 the conversion is a no-op.
>> >
>> > G
>> >
>> > On Thu, Sep 20, 2012 at 4:17 PM, Michael Snoyman <michael at snoyman.com>
>> > wrote:
>> >>
>> >> On Thu, Sep 20, 2012 at 2:10 PM, Michael Snoyman <michael at snoyman.com>
>> >> wrote:
>> >> > On Thu, Sep 20, 2012 at 11:41 AM, Kazu Yamamoto <kazu at iij.ad.jp>
>> wrote:
>> >> >> Hello,
>> >> >>
>> >> >> ByteString is an array of Word8 but it seems to me that people tend
>> to
>> >> >> use the Char interface with Data.ByteString.Char8 instead of Word8
>> >> >> interface with Data.ByteString. Since the functions defined in
>> >> >> Data.ByteString.Char8 converts Word8 to Char and Char to Word8, it
>> has
>> >> >> unnecessary overhead. Yes, the overhead is ignorable in many cases,
>> >> >> but I would like to remove it for high performance server.
>> >> >>
>> >> >> Why do people use Data.ByteString.Char8? I guess that there are two
>> >> >> reasons:
>> >> >>
>> >> >> - There are no standard utility functions for Word8 such as
>> "isUpper"
>> >> >> - Numeric literal (e.g 72 for 'H') is not readable
>> >> >>
>> >> >> To fix these problems, I implemented the Data.Word8 module and
>> >> >> uploaded the word8 library to Hackage:
>> >> >>
>> >> >>
>> >> >>
>> http://hackage.haskell.org/packages/archive/word8/0.0.0/doc/html/Data-Word8.html
>> >> >>
>> >> >> If Michael and Bas like this, I would like to modify warp and
>> >> >> case-insensitive to use the word8 library. What do people think
>> this?
>> >> >>
>> >> >> My concern is that character names start with "_". Some people would
>> >> >> dislike this convention. But I have not a better idea at this
>> moment.
>> >> >> Suggestions are welcome.
>> >> >>
>> >> >> --Kazu
>> >> >>
>> >> >> _______________________________________________
>> >> >> web-devel mailing list
>> >> >> web-devel at haskell.org
>> >> >> http://www.haskell.org/mailman/listinfo/web-devel
>> >> >
>> >> > Sounds good to me. I put together a simple benchmark to compare the
>> >> > performance of toLower, and the results are encouraging:
>> >> >
>> >> > benchmarking Char8
>> >> > mean: 38.04527 us, lb 37.94080 us, ub 38.12774 us, ci 0.950
>> >> > std dev: 470.9770 ns, lb 364.8254 ns, ub 748.3015 ns, ci 0.950
>> >> >
>> >> > benchmarking Word8
>> >> > mean: 4.807265 us, lb 4.798199 us, ub 4.816563 us, ci 0.950
>> >> > std dev: 47.20958 ns, lb 41.51181 ns, ub 55.07049 ns, ci 0.950
>> >> >
>> >> > I want to try throwing one more idea into the mix, I'll post with
>> >> > updates when I have them.
>> >> >
>> >> > So to answer your question: I'd be happy to include word8 in warp :).
>> >> >
>> >> > Michael
>> >> >
>> >> >
>> >> > {-# LANGUAGE OverloadedStrings #-}
>> >> > import Criterion.Main
>> >> > import qualified Data.ByteString as S
>> >> > import qualified Data.ByteString.Char8 as S8
>> >> > import qualified Data.Char
>> >> > import qualified Data.Word8
>> >> >
>> >> > main :: IO ()
>> >> > main = do
>> >> >     input <- S.readFile "bench.hs"
>> >> >     defaultMain
>> >> >         [ bench "Char8" $ whnf (S.length . S8.map Data.Char.toLower)
>> >> > input
>> >> >         , bench "Word8" $ whnf (S.length . S.map Data.Word8.toLower)
>> >> > input
>> >> >         ]
>> >>
>> >> I tried implementing a more low-level approach to try and avoid the
>> >> Word8 boxing. The results improved a bit, but not significantly:
>> >>
>> >>
>> >> benchmarking Char8
>> >> mean: 318.2341 us, lb 314.5367 us, ub 320.4834 us, ci 0.950
>> >> std dev: 14.48230 us, lb 10.00946 us, ub 21.22126 us, ci 0.950
>> >> found 9 outliers among 100 samples (9.0%)
>> >>   8 (8.0%) low severe
>> >> variance introduced by outliers: 43.472%
>> >> variance is moderately inflated by outliers
>> >>
>> >> benchmarking Word8
>> >> mean: 35.79037 us, lb 35.66547 us, ub 35.92601 us, ci 0.950
>> >> std dev: 665.5299 ns, lb 599.3413 ns, ub 741.6474 ns, ci 0.950
>> >> variance introduced by outliers: 11.349%
>> >> variance is moderately inflated by outliers
>> >>
>> >> benchmarking bsToLower
>> >> mean: 31.49299 us, lb 31.32314 us, ub 31.65027 us, ci 0.950
>> >> std dev: 835.2251 ns, lb 744.4337 ns, ub 946.1789 ns, ci 0.950
>> >> variance introduced by outliers: 20.925%
>> >> variance is moderately inflated by outliers
>> >>
>> >> Perhaps someone with more experience with this level of optimization
>> >> would be able to improve the algorithm:
>> >>
>> >> https://gist.github.com/3756212
>> >>
>> >> Michael
>> >>
>> >> _______________________________________________
>> >> web-devel mailing list
>> >> web-devel at haskell.org
>> >> http://www.haskell.org/mailman/listinfo/web-devel
>> >
>> >
>> >
>> >
>> > --
>> > Gregory Collins <greg at gregorycollins.net>
>>
>
>
>
> --
> Gregory Collins <greg at gregorycollins.net>
>

Hmm... I don't get your results.

benchmarking Char8
mean: 394.2475 us, lb 393.1611 us, ub 395.3824 us, ci 0.950
std dev: 5.674103 us, lb 4.574321 us, ub 7.548278 us, ci 0.950
found 16 outliers among 100 samples (16.0%)
  1 (1.0%) low severe
  4 (4.0%) low mild
  6 (6.0%) high mild
  5 (5.0%) high severe
variance introduced by outliers: 7.517%
variance is slightly inflated by outliers

benchmarking Char8 toLowerC
mean: 81.19748 us, lb 80.95403 us, ub 81.40814 us, ci 0.950
std dev: 1.154865 us, lb 977.5925 ns, ub 1.497224 us, ci 0.950
found 2 outliers among 100 samples (2.0%)
  1 (1.0%) low severe
variance introduced by outliers: 7.506%
variance is slightly inflated by outliers

benchmarking Word8
mean: 43.01692 us, lb 42.94030 us, ub 43.09647 us, ci 0.950
std dev: 401.2451 ns, lb 362.3989 ns, ub 458.7243 ns, ci 0.950

benchmarking bsToLower
mean: 36.61481 us, lb 36.46137 us, ub 36.79378 us, ci 0.950
std dev: 850.7579 ns, lb 717.1316 ns, ub 1.004895 us, ci 0.950
found 16 outliers among 100 samples (16.0%)
  2 (2.0%) low mild
  10 (10.0%) high mild
  4 (4.0%) high severe
variance introduced by outliers: 17.062%
variance is moderately inflated by outliers

I'm compiling with -O2 and running on 7.4.1, 64-bit Linux. I'm uncertain
what would lead to such a significant difference in our runtimes. Any
chance you can include Word8 in your run?

Michael
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/web-devel/attachments/20120920/fea3b24a/attachment.htm>