Use `Builder` instead of `String` #18

parsonsmatt · 2022-12-11T23:14:14Z

Fixes #16

This PR uses Data.ByteString.Builder instead of String for HTML fragments

Also uses difference lists to avoid the ++ penalty

There's no benchmark on the library, so I can't provide direct results. However, comparing this to my CPS WriterT branch on haddock, I'm seeing some nice improvements, particularly for such a local change:

With just the CPS WriterT

!!! ppHtml: finished in 574.35 milliseconds, allocated 1592.523 megabytes
*** Deleting temp dirs:
  26,145,652,864 bytes allocated in the heap
   4,170,952,440 bytes copied during GC
     278,830,600 bytes maximum residency (18 sample(s))
       5,591,544 bytes maximum slop
             621 MiB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0      6230 colls,     0 par    2.444s   2.448s     0.0004s    0.0040s
  Gen  1        18 colls,     0 par    1.423s   1.423s     0.0791s    0.2157s

  TASKS: 5 (1 bound, 4 peak workers (4 total), using -N1)

  SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

  INIT    time    0.001s  (  0.000s elapsed)
  MUT     time   10.466s  ( 11.403s elapsed)
  GC      time    3.867s  (  3.871s elapsed)
  EXIT    time    0.001s  (  0.006s elapsed)
  Total   time   14.334s  ( 15.280s elapsed)

  Alloc rate    2,498,258,001 bytes per MUT second

  Productivity  73.0% of total user, 74.6% of total elapsed

Documentation created:
/home/matt/Projects/persistent/dist-newstyle/build/x86_64-linux/ghc-9.4.3/persistent-test-2.13.1.3/doc/html/persistent-test/index.html
cabal haddock --haddock-options "-v2 +RTS -s -RTS --optghc=\"-v2\""    16.09s user 1.53s system 98% cpu 17.834 total

HTML allocations: 1,592MB
HTML time: 574ms
Time: 17.834s
Mem in use: 621MB
Allocated: 26.145GB

Using a `Builder` variant of `xhtml`

!!! ppHtml: finished in 298.89 milliseconds, allocated 1578.839 megabytes

  26,199,628,152 bytes allocated in the heap
   3,842,361,072 bytes copied during GC
     204,699,600 bytes maximum residency (17 sample(s))
       5,185,792 bytes maximum slop
             547 MiB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0      6139 colls,     0 par    2.358s   2.362s     0.0004s    0.0039s
  Gen  1        17 colls,     0 par    1.168s   1.169s     0.0688s    0.1587s

  TASKS: 5 (1 bound, 4 peak workers (4 total), using -N1)

  SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

  INIT    time    0.001s  (  0.000s elapsed)
  MUT     time   10.425s  ( 11.357s elapsed)
  GC      time    3.526s  (  3.531s elapsed)
  EXIT    time    0.001s  (  0.002s elapsed)
  Total   time   13.953s  ( 14.890s elapsed)

  Alloc rate    2,513,036,906 bytes per MUT second

  Productivity  74.7% of total user, 76.3% of total elapsed

Documentation created:
/home/matt/Projects/persistent/dist-newstyle/build/x86_64-linux/ghc-9.4.3/persistent-test-2.13.1.3/doc/html/persistent-test/index.html
cabal haddock --haddock-options "-v2 +RTS -s -RTS --optghc=\"-v2\""    14.38s user 0.89s system 100% cpu 15.236 total

HTML allocations: 1,578MB (-14MB) negligible
HTML time: 299ms (-275ms) (48% reduction)
Mem in use: 547MB (-74MB) (12% reduction)

Surprisingly, overall allocations are about the same. I'd have expected the allocations to be much less, since the overhead of a Builder is smaller than a String.

The reduced memory in use is stable across haddock runs. I'm not entirely sure why that's the case, given that allocations are basically unchanged.

This reverts commit 75f992d.

This reverts commit 79b8d5f.

This reverts commit c19f6cd.

This reverts commit 7310148.

cdornan · 2022-12-12T16:08:12Z

This is awesome @parsonsmatt — I am completely sold on this being the right way to go and am entirely concerned about not breaking anything.

What are the risks as you see it?

parsonsmatt · 2022-12-13T01:24:38Z

Well, after doing some benchmarking and profiling, I'm unconvinced this is the right approach.

It is a noticeable improvement. But haddock's HTML rendering in persistent-test is dominated by link generation - anchor ! [href str]. It's doing a ton of fixChar, which ends up taking an inordinate amount of time. I'm also suspicious that it may be repeating this.

So I want to do a bit more benchmarking before I commit this in

cdornan · 2022-12-13T02:54:39Z

By all means! My main concern remains avoiding breakage.

parsonsmatt · 2022-12-13T14:19:16Z

Do you mean like API break? Or breaking change in behvaior?

There isn't a test suite. I suppose I could diff the result of a Haddock run with this path and before.

cdornan · 2022-12-13T15:15:45Z

I mean breaking changes in behaviour and I am concerned because we have no test coverage.

So I really have to rely on good old fashioned engineering judgement — yours! If you think the risks are reasonable then I am good with that.

This reverts commit 03a4346.

cdornan · 2022-12-19T03:09:57Z

@parsonsmatt do you need anything from me? (All good on my side — just checking I am not blocking anything.)

parsonsmatt · 2022-12-20T00:56:09Z

No, I just want to ensure this is actually a performance boon on Haddock. I haven't been able to verify that it speeds anything up or that it's correct yet.

cdornan · 2022-12-20T01:08:18Z

all cool — just ping me if you need anything

parsonsmatt · 2022-12-21T19:46:38Z

Text/XHtml/Internals.hs

  where
      close = if empty then " />" else ">"

-      shownAttrs = concat [' ':showPair attr | attr <- attrs ]
+      shownAttrs = foldMap (\attr -> charUtf8 ' ' <> showPair attr) attrs


In my equivalence testing, the attributes are showing up in reverse order. Weird. The difference should be pretty small.

concat [ k x | x <- xs ] is equal to concat $ map k xs, which is concatMap k xs, and concatMap = foldMap when m ~ [b], as it is here, so the real diff is

-foldMap (\attr -> ' ' : showPair attr) attrs +foldMap (\attr -> charUtf8 ' ' <> showPair attr) attrs

So the rendering isn't the issue.

parsonsmatt · 2022-12-21T19:49:54Z

Text/XHtml/Internals.hs

-              addAttrs (html@(HtmlTag { markupAttrs = attrs }) )
-                            = html { markupAttrs = attrs ++ attr }


So here we have attrs ++ attr, with attr being the new thing. So:

(anchor ! [href "asdf"]) ! [theclass "woop"]

should evaluate to:

(anchor ! [href "asdf"]) ! [theclass "asdf"] (Html { attrs = [href "asdf"] }) ! [theclass "asdf"] (Html { attrs = [href "asdf"] ++ [theclass "asdf"] })

parsonsmatt · 2022-12-21T19:59:29Z

Text/XHtml/Internals.hs

+            case html of
+                HtmlTag { markupAttrs = attrs, .. } ->
+                    HtmlTag
+                        { markupAttrs = attrs . (++ attr)


But here, we have:

(anchor ! [href "asdf"]) ! [theclass "qwer"] ==> (HtmlTag { markupAttrs = id } ! [href "asdf"]) ! [theclass "qwer"] ==> HtmlTag { markupAttrs = id . (++ [href "asdf"]) } ! [theclass "qwer"] ==> HtmlTag { markupAttrs = id . (++ [href "asdf"]) . (++ [theclass "qwer"]) }

When we go to render, we apply [] to this. GHCI makes that:

λ> id . (++ ["asdf"]) . (++ ["qwer"]) $ [] ["qwer","asdf"]

Which is - hm, a bit surprising!

id . (++ xs) . (++ ys) $ [] -- delete id (++ xs) . (++ ys) $ [] -- replace `.` with `$` (++ xs) $ (++ ys) [] -- inline operator section (++ xs) $ [] ++ ys -- inline operator ([] ++ ys) ++ xs

The dlist package defines fromList as UnsafeDList . (++) and append as UnsafeDList $ unsafeApplyDList xs . unsafeApplyDList ys.

fromList xs = UnsafeDList . (++) $ xs fromList xs = UnsafeDList $ (++) xs fromList xs = UnsafeDList (xs ++)

So, yeah, I converted attr incorrectly here.

parsonsmatt · 2022-12-21T20:22:34Z

Verified that there's no diff for persistent generated documentation with this patch and without on haddock 🎉

Final performance improvement:

Comparing Haddock Head and the most recent, we get:

	Haddock Head	`xhtml` Builder	Absolute Difference	Relative Change
HTML allocations	1134 MB	1141 MB	+7 MB	0.6% worse
HTML time:	380 ms	198 ms	-182 ms	47.9% improvement
Total Memory:	554 MB	466 MB	-88 MB	15.9% improvement
Total Allocated:	16.0 GB	16.0 GB	0	No change
Max residency:	238 MB	195 MB	-43 MB	18.1% improvement
Total Time:	10.88 s	6.526s s	-4.354 s	40% improvement

Pretty pleased with these results.

parsonsmatt · 2022-12-21T20:24:56Z

@cdornan I believe this is ready for merge and release

parsonsmatt · 2022-12-21T20:33:49Z

Unfortunately, this API is unpleasant with OverloadedStrings. Can see in the Haddock PR: https://github.com/haskell/haddock/pull/1546/files

Because many functions accept HTML a => a, OverloadedStrings causes a string literal to be unable to resolve without a type application or signature.

parsonsmatt · 2022-12-23T01:52:22Z

OK, this is really frustrating!

I can't reproduce the performance findings. In fact, when I try now, the Builder variant is considerably worse, on all metrics.

Going to close this out for now until I can figure out what's going on.

cdornan · 2022-12-23T02:24:48Z

@parsonsmatt i am so sorry! And sorry I could not be of more help and thanks for looking into this. I hope you have a good break.

parsonsmatt · 2022-12-23T03:19:24Z

I'm thinking it may be an issue with GHC 9.4.2, actually? GHC 9.4.3 shows a big speedup. But the work codebase uses GHC 9.4.2, and I can't reproduce the performance benefits with 9.4.2.

cdornan · 2022-12-23T15:51:35Z

That could explain it. Feel free to reopen once your confidence is restored.

parsonsmatt added 8 commits December 11, 2022 13:04

Use ByteString Builder instead of String

c015aec

Use DList too

4f3111b

Add Text instance

09f6636

Don't force list more than necessary

4b29de4

inline stuff

75f992d

Revert "inline stuff"

c785280

This reverts commit 75f992d.

no inlining pls

62396e1

factor a thing out

762b55c

parsonsmatt changed the title ~~Mattp/builder~~ Use Builder instead of String Dec 11, 2022

parsonsmatt added 6 commits December 11, 2022 16:35

faster isNoHtml

c19f6cd

wow that's slower!

79b8d5f

Revert "wow that's slower!"

bbc78cf

This reverts commit 79b8d5f.

Revert "faster isNoHtml"

38a41d4

This reverts commit c19f6cd.

regular list instead of dlist

7310148

Revert "regular list instead of dlist"

03df931

This reverts commit 7310148.

parsonsmatt mentioned this pull request Dec 12, 2022

Use the Builder patch for xhtml haskell/haddock#1546

Closed

Try with a Seq instead of a dlist

03a4346

parsonsmatt added 2 commits December 13, 2022 18:07

major bump

6699a6a

Revert "Try with a Seq instead of a dlist"

b911311

This reverts commit 03a4346.

parsonsmatt commented Dec 21, 2022

View reviewed changes

Fix attribute ordering

0c9a8ae

Changelog entry

47a9e31

parsonsmatt closed this Dec 23, 2022

FinleyMcIlwaine mentioned this pull request Jul 4, 2023

Switch to Builder and Text #19

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Use `Builder` instead of `String` #18

Use `Builder` instead of `String` #18

parsonsmatt commented Dec 11, 2022 •

edited

cdornan commented Dec 12, 2022

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parsonsmatt commented Dec 23, 2022

cdornan commented Dec 23, 2022

		addAttrs (html@(HtmlTag { markupAttrs = attrs }) )
		= html { markupAttrs = attrs ++ attr }

Use Builder instead of String #18

Use Builder instead of String #18

Conversation

parsonsmatt commented Dec 11, 2022 • edited

With just the CPS WriterT

Using a Builder variant of xhtml

cdornan commented Dec 12, 2022

parsonsmatt commented Dec 13, 2022

cdornan commented Dec 13, 2022

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cdornan commented Dec 23, 2022

Use `Builder` instead of `String` #18

Use `Builder` instead of `String` #18

parsonsmatt commented Dec 11, 2022 •

edited

Using a `Builder` variant of `xhtml`