[gambit-list] Slow Bit Hacking with c-lambda

Mikael mikael.rcv at gmail.com
Sun Nov 4 17:38:22 EST 2012


Ah, also throw in the following:
 * (declare (not interrupts-enabled))

   This might be a big deal - when it's off, Gambit doesn't produce any
hooks for stack overflow or thread system interrupts but executes your code
according to a typical C model

 * (declare (standard-bindings) (extended-bindings)) too?


What is the performance you get from Gambit now, and what kind of
performance is it you want to get?


2012/11/4 tcl super dude <tcleval at gmail.com>

> I assumed I could get a bit of performance improvement over min procedure
> because I don't do any branch. I' thought  min-integer to be at least close
> to gambit-c time. The problem is that those operations and a few more are
> performed thousands of times. Gambit loops are usually 2x slower than C, so
> I hoped I could improve some basic operations as I only perform them on
> integers. I don't Understand how a simple shift to extract the lower bits
> could make so much difference. Maybe if someone point me to the
> implementation of min and abs on gambit, I can understand the difference. I
> ve looked for these procedures on gambit's source but could not point it
> out.
>
> I'll try to implement them using vectors and see what happens.
>
> now compiled with (block):
>
>
> abs:
>
> (time (let loop-i ((i 0)) (cond ((fx< i 100000) (set! result (abs i))
> (loop-i (fx+ 1 i))))))
>     2 ms real time
>
>     3 ms cpu time (3 user, 0 system)
>
>     no collections
>
>     no bytes allocated
>
>     no minor faults
>
>     no major faults
>
> abs-integer:
>
> (time (let loop-j ((j 0)) (cond ((fx< j 100000) (set! result (abs-integer
> j)) (loop-j (fx+ 1 j))))))
>     19 ms real time
>
>     20 ms cpu time (17 user, 3 system)
>
>     no collections
>
>     no bytes allocated
>
>     2 minor faults
>
>     no major faults
>
> min:
>
> (time (let loop-i ((i 0)) (cond ((fx< i 100000) (set! result (min i
> result)) (loop-i (fx+ 1 i))))))
>     2 ms real time
>
>     3 ms cpu time (0 user, 3 system)
>
>     no collections
>
>     no bytes allocated
>
>     no minor faults
>     no major faults
> min-integer:
> (time (let loop-j ((j 0)) (cond ((fx< j 100000) (set! result (min-integer
> j result)) (loop-j (fx+ 1 j))))))
>     27 ms real time
>     27 ms cpu time (27 user, 0 system)
>     no collections
>     no bytes allocated
>     no minor faults
>     no major faults
>
>
> On Sun, Nov 4, 2012 at 5:15 PM, Mikael <mikael.rcv at gmail.com> wrote:
>
>> First, please add (declare (block)) and re-compile, this way Gambit won't
>> need to re-look up the procedures in the global namespace that you call, on
>> each invocation. Please report what kind of improvement you got with this.
>>
>>
>> Now just to make this round of emails complete:
>>
>> What would be good/very good performance in your view?
>>
>> Could you send jobs in some kind of batch format to C?
>>
>> Note that Gambit-internal fxnum variables have a special encoding (the
>> lowermost two(?) bits are object type identifier, which are shifted out
>> when converting them to C int), this takes a little bit of time.
>>
>> If for instance you make u32vectors/s32vectors/etc. [and send batch ops
>> made on those to C to be performed etc.] then you can just read out the
>> content of those vectors 'raw' in C, there's no interconversion there.
>>
>> Brgds
>>
>> 2012/11/4 tcl super dude <tcleval at gmail.com>
>>
>>> Hi everyone,
>>>
>>> I have been working on an image processing library that I want to use on
>>> android. I know that performance is a bit of a problem on image processing,
>>> so I started to study some bit hacking to improve the performance on my
>>> integer operations.  My problem now is that I don't know why my c-lambdas
>>> take so much time to execute. All operations take constant time and there
>>> is no branching. Probably is some sort of conversion time between C types
>>> and GAMBIT types. I expected min-integer and abs-integer to be a lot faster
>>> than min and abs, respectively. Any help is appreciated.
>>>
>>> URL REFERENCE:
>>> http://graphics.stanford.edu/~seander/bithacks.html#IntegerAbs
>>> http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
>>>
>>>
>>> MY ENVIRONMENT:
>>> Linux casa 3.6.4-1-ARCH #1 SMP PREEMPT Mon Oct 29 15:13:56 CET 2012 i686
>>> GNU/Linux
>>>
>>> gcc -v
>>> Using built-in specs.
>>> COLLECT_GCC=gcc
>>> COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-pc-linux-gnu/4.7.2/lto-wrapper
>>> Target: i686-pc-linux-gnu
>>> Configured with: /build/src/gcc-4.7.2/configure --prefix=/usr
>>> --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
>>> --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
>>> --enable-threads=posix --with-system-zlib --enable-__cxa_atexit
>>> --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
>>> --enable-libstdcxx-time --enable-gnu-unique-object --enable-linker-build-id
>>> --with-ppl --enable-cloog-backend=isl --disable-ppl-version-check
>>> --disable-cloog-version-check --enable-lto --enable-gold
>>> --enable-ld=default --enable-plugin --with-plugin-ld=ld.gold
>>> --with-linker-hash-style=gnu --disable-multilib --disable-libssp
>>> --disable-build-with-cxx --disable-build-poststage1-with-cxx
>>> --enable-checking=release
>>> Thread model: posix
>>> gcc version 4.7.2 (GCC)
>>>
>>> Gambit v4.6.6 (SINGLE HOST and GCC extensions enabled)
>>>
>>>
>>> SCHEME CODE: compiled with ---> gambitc -exe   bithacks.scm
>>>
>>> ;; bithacks.scm
>>>
>>>
>>> (declare
>>>  (not safe)
>>>  (fixnum)
>>>  (inline)
>>>  (inline-primitives))
>>>
>>> ;; INTEGER ABSOLUTE
>>> (define abs-integer
>>>   (c-lambda (int) int
>>>     "// we want to find the absolute value of arg1
>>>      int const mask = ___arg1 >> sizeof(int) * CHAR_BIT - 1;
>>>      ___result = (___arg1 + mask) ^ mask;"))
>>>
>>>
>>> (define min-integer
>>>   (c-lambda (int int) int
>>>     "// find the smaller of arg1 arg2
>>>      ___result = ___arg2 ^ ((___arg1 ^ ___arg2) & -(___arg1 <
>>> ___arg2));"))
>>>
>>> (define (test-abs)
>>>   (let ((result 0))
>>>     (begin
>>>       (display "abs:\n")
>>>       (time
>>>        (let loop-i ((i 0))
>>>          (cond ((fx< i 100000)
>>>                 (set! result (abs i))
>>>                 (loop-i (fx+ 1 i))))))
>>>       (display "abs-integer:\n")
>>>       (time
>>>        (let loop-j ((j 0))
>>>          (cond ((fx< j 100000)
>>>                 (set! result (abs-integer j))
>>>                 (loop-j (fx+ 1 j)))))))))
>>>
>>> (define (test-min)
>>>   (let ((result 0))
>>>     (begin
>>>       (display "min:\n")
>>>       (time
>>>        (let loop-i ((i 0))
>>>          (cond ((fx< i 100000)
>>>                 (set! result (min i result))
>>>                 (loop-i (fx+ 1 i))))))
>>>       (display "min-integer:\n")
>>>       (time
>>>        (let loop-j ((j 0))
>>>          (cond ((fx< j 100000)
>>>                 (set! result (min-integer j result))
>>>                 (loop-j (fx+ 1 j)))))))))
>>>
>>> ;; run tests
>>>
>>> (test-abs)
>>> (test-min)
>>>
>>> ;;;;;;;;;;;;;;;;;;;;;; RESULTS;;;;;;;;;;;;;;;;;;;;;
>>>
>>> abs:
>>> (time (let loop-i ((i 0)) (cond ((fx< i 100000) (set! result (abs i))
>>> (loop-i (fx+ 1 i))))))
>>>     2 ms real time
>>>     3 ms cpu time (3 user, 0 system)
>>>     no collections
>>>     no bytes allocated
>>>     no minor faults
>>>     no major faults
>>> abs-integer:
>>> (time (let loop-j ((j 0)) (cond ((fx< j 100000) (set! result
>>> (abs-integer j)) (loop-j (fx+ 1 j))))))
>>>     22 ms real time
>>>     23 ms cpu time (23 user, 0 system)
>>>     no collections
>>>     no bytes allocated
>>>     2 minor faults
>>>     no major faults
>>> min:
>>> (time (let loop-i ((i 0)) (cond ((fx< i 100000) (set! result (min i
>>> result)) (loop-i (fx+ 1 i))))))
>>>      2 ms real time
>>>     3 ms cpu time (0 user, 3 system)
>>>     no collections
>>>     no bytes allocated
>>>     no minor faults
>>>     no major faults
>>> min-integer:
>>> (time (let loop-j ((j 0)) (cond ((fx< j 100000) (set! result
>>> (min-integer j result)) (loop-j (fx+ 1 j))))))
>>>     28 ms real time
>>>     30 ms cpu time (27 user, 3 system)
>>>     no collections
>>>     no bytes allocated
>>>     no minor faults
>>>     no major faults
>>>
>>>
>>> _______________________________________________
>>> Gambit-list mailing list
>>> Gambit-list at iro.umontreal.ca
>>> https://webmail.iro.umontreal.ca/mailman/listinfo/gambit-list
>>>
>>>
>>
>
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