5 ms·

Writing Performance Sensitive OCaml Code

84 points by amirmc 13y ago

octo_t 13y ago
I'm surprised the compiler goes straight to assembly, rather than targeting LLVM (most native programming languages) or C- (what GHC does/did)
- tych0 13y ago
  Why? Ocaml was around long before LLVM, and GHC has a mode where you can emit assembly (and one where you can emit LLVM as well).
- deleted 13y ago
  [deleted]
- omaranto 13y ago
  Most compilers target LLVM? That doesn't sound right. Maybe most compilers written in the last five years or so.
- rwmj 13y ago
  There's an OCaml LLVM backend [1]. The author found a number of issues with LLVM [2] although this could be overcome. The real problem is that the low-level object format is completely different which would break all OCaml extensions written in C (eg. any extension that links to an external C library). Plus the current code generators are really fast and cover all common architectures anyway so there's not much point. [1] https://github.com/colinbenner/ocamlllvm https://github.com/colinbenner/ocamlllvm [2] http://oud.ocaml.org/2012/abstracts/oud2012-paper7.pdf http://oud.ocaml.org/2012/abstracts/oud2012-paper7.pdf
- profquail 13y ago
  FYI, it's C-- (not C-): https://en.wikipedia.org/wiki/C-- https://en.wikipedia.org/wiki/C--
- masklinn 13y ago
  > I'm surprised the compiler goes straight to assembly, rather than targeting LLVM (most native programming languages) Most native programming languages historically don't, and OCaml predates LLVM by a good 7 years. > or C- (what GHC does/did) Cmm is an intermediate language specific to GHC before the backend[1], GHC's default backend is a native generator. [1] or more precisely "an other" intermediate language, since there's also Core.
- freyrs3 13y ago
  > , rather than targeting LLVM (most native programming languages) Native languages targeting LLVM are the exception not the norm. The vast majority of native compilers do emit assembly. [1] http://llvm.org/ProjectsWithLLVM/ http://llvm.org/ProjectsWithLLVM/
- MostAwesomeDude 13y ago
  You might be surprised to learn that there are languages that are agnostic in what they target.
- kenko 13y ago
  Why? Going to llvm constrains you to do llvm's models. (Also, the timing issue mentioned by a sibling.)
chollida1 13y ago
Wow, the first 5 comments on this were about should they use LLVM:) The author is currently writing a book about OCaml that is now available in alpha format from here: http://www.realworldocaml.org/ http://www.realworldocaml.org/ I've finished the first part and looked at the compiler section, and I love this book, no affiliation in any way.
- KaeseEs 13y ago
  On the one hand, OCaml is a very interesting language and I welcome a good book about it in the vein of Real World Haskell. On the other hand, it is the height of treason for O'Reilly to make a book with a camel on the cover that isn't about Perl :v
  - amirmc 13y ago
    They're different species of Camel. The Bactrian has two humps and the Dromedary has one (among other differences).
  - flyinRyan 13y ago
    When someone/thing dies, it's ok to reuse their Jersey eventually.
    - Mithaldu 13y ago
      HMMMM. http://www.indeed.com/jobtrends?q=perl%2C+python%2C+ruby%2C+php%2C+ocaml&l= http://www.indeed.com/jobtrends?q=perl%2C+python%2C+ruby%2C+...
      - flyinRyan 13y ago
        Nice hand-picked rebuttal. Can I play too? http://www.indeed.com/jobtrends?q=perl%2C+Java%2C+C%2B%2B%2C+C%2C+C%23%2C+go&l= http://www.indeed.com/jobtrends?q=perl%2C+Java%2C+C%2B%2B%2C... HMMMM indeed.
        13y ago
edwintorok 13y ago
This is a good collection of performance tips, although I'd use Unix.gettimeofday instead of RDTSC (RDTSC needs additional care on multicore). Also it is interesting that OCaml's tutorial has a section on performance (that is not something common in other language tutorials): http://ocaml.org/tutorials/performance_and_profiling.html http://ocaml.org/tutorials/performance_and_profiling.html
toolslive 13y ago
This is a good overview of performance 'idiosyncrasies'. For profiling, I tend to use valgrind's callgrind which is easier than instrumenting the code by hand.

84 points by amirmc 13y ago

I'm surprised the compiler goes straight to assembly, rather than targeting LLVM (most native programming languages) or C- (what GHC does/did)

tych0 13y ago
Why? Ocaml was around long before LLVM, and GHC has a mode where you can emit assembly (and one where you can emit LLVM as well).
deleted 13y ago
[deleted]
omaranto 13y ago
Most compilers target LLVM? That doesn't sound right. Maybe most compilers written in the last five years or so.
rwmj 13y ago
There's an OCaml LLVM backend [1]. The author found a number of issues with LLVM [2] although this could be overcome. The real problem is that the low-level object format is completely different which would break all OCaml extensions written in C (eg. any extension that links to an external C library). Plus the current code generators are really fast and cover all common architectures anyway so there's not much point. [1] https://github.com/colinbenner/ocamlllvm https://github.com/colinbenner/ocamlllvm [2] http://oud.ocaml.org/2012/abstracts/oud2012-paper7.pdf http://oud.ocaml.org/2012/abstracts/oud2012-paper7.pdf
profquail 13y ago
FYI, it's C-- (not C-): https://en.wikipedia.org/wiki/C-- https://en.wikipedia.org/wiki/C--
masklinn 13y ago
> I'm surprised the compiler goes straight to assembly, rather than targeting LLVM (most native programming languages) Most native programming languages historically don't, and OCaml predates LLVM by a good 7 years. > or C- (what GHC does/did) Cmm is an intermediate language specific to GHC before the backend[1], GHC's default backend is a native generator. [1] or more precisely "an other" intermediate language, since there's also Core.
freyrs3 13y ago
> , rather than targeting LLVM (most native programming languages) Native languages targeting LLVM are the exception not the norm. The vast majority of native compilers do emit assembly. [1] http://llvm.org/ProjectsWithLLVM/ http://llvm.org/ProjectsWithLLVM/
MostAwesomeDude 13y ago
You might be surprised to learn that there are languages that are agnostic in what they target.
kenko 13y ago
Why? Going to llvm constrains you to do llvm's models. (Also, the timing issue mentioned by a sibling.)

chollida1 13y ago

Wow, the first 5 comments on this were about should they use LLVM:) The author is currently writing a book about OCaml that is now available in alpha format from here: http://www.realworldocaml.org/ http://www.realworldocaml.org/ I've finished the first part and looked at the compiler section, and I love this book, no affiliation in any way.

KaeseEs 13y ago
On the one hand, OCaml is a very interesting language and I welcome a good book about it in the vein of Real World Haskell. On the other hand, it is the height of treason for O'Reilly to make a book with a camel on the cover that isn't about Perl :v
- amirmc 13y ago
  They're different species of Camel. The Bactrian has two humps and the Dromedary has one (among other differences).
- flyinRyan 13y ago
  When someone/thing dies, it's ok to reuse their Jersey eventually.
  - Mithaldu 13y ago
    HMMMM. http://www.indeed.com/jobtrends?q=perl%2C+python%2C+ruby%2C+php%2C+ocaml&l= http://www.indeed.com/jobtrends?q=perl%2C+python%2C+ruby%2C+...
    - flyinRyan 13y ago
      Nice hand-picked rebuttal. Can I play too? http://www.indeed.com/jobtrends?q=perl%2C+Java%2C+C%2B%2B%2C+C%2C+C%23%2C+go&l= http://www.indeed.com/jobtrends?q=perl%2C+Java%2C+C%2B%2B%2C... HMMMM indeed.
      - 13y ago

edwintorok 13y ago

This is a good collection of performance tips, although I'd use Unix.gettimeofday instead of RDTSC (RDTSC needs additional care on multicore). Also it is interesting that OCaml's tutorial has a section on performance (that is not something common in other language tutorials): http://ocaml.org/tutorials/performance_and_profiling.html http://ocaml.org/tutorials/performance_and_profiling.html

toolslive 13y ago

This is a good overview of performance 'idiosyncrasies'. For profiling, I tend to use valgrind's callgrind which is easier than instrumenting the code by hand.