60% performance regression in continuation-heavy code between 6.12 and 7

I have a JSON parsing library whose performance has regressed by a little over 60% between 6.12.3 and the current head of the 7.0 branch.

The library uses my attoparsec parsing library, which is written in a heavily continuation-based style.

Building the code

Reproducing the problem is pretty easy.

You need two git repos:

git clone git://github.com/bos/attoparsec
git clone git://github.com/mailrank/aeson

They're easily built:

(cd attoparsec && cabal install)
(cd aeson && cabal install)

Measuring performance

Inside the aeson repo are some benchmarks, of which AesonParse is the only interesting one for our purposes.

cd aeson/benchmarks && make AesonParse

There's also prepackaged test data, so you can run a benchmark on the spot.

./AesonParse 1000 json-data/twitter100.json

This program accepts a number of loop iterations as its first argument, and a data file as its second. It prints its execution time, so a smaller number indicates better performance.

Performance with 6.12.3

Here's what I see with 6.12.3, on my MacBook Pro running OS X 10.6.5.

$ ./AesonParse 1000 json-data/twitter100.json 
json-data/twitter100.json:
  1000 good, 1.847631s

This number is good - it's about as fast as Python's C-based json parser.

Performance with GHC 7

You can pass a ghc argument to make to build the benchmark with a different compiler.

make clean
make AesonParse ghc=/usr/local/ghc/7/bin/ghc

And with the benchmark rebuilt, here's the performance:

$ ./AesonParse7 1000 json-data/twitter100.json 
json-data/twitter100.json:
  1000 good, 2.939818s

This is one of the very few instances I've seen of a performance regression with GHC 7, and unfortunately it's very large.

Please let me know what other information I can provide.

Trac metadata

Trac field	Value
Version	7.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture