On 16/09/2012 15:34, Neil Van Dyke wrote:
1. Use statistical profiler to see who is actually eating the time:
http://doc.racket-lang.org/profile/index.html Increasing the sampling
resolution can help.
This is what I get - only quoting the highest self pct:
Profiling results
-----------------
Total cpu time observed: 19244ms (out of 19495ms)
Number of samples taken: 1541 (once every 12ms)
========================================================
for-each [5] 47.2%
loop [3] 52.8%
[5] 8669(45.0%) 5286(27.5%) for-each
.../collects/racket/private/map.rkt:48:13
for-each [5] 47.2%
loop [3] 46.5%
??? [7] 1.4%
I've looked at the code and find nothing revealing
46 (define for-each2
47 (let ([for-each
48 (case-lambda
49 [(f l)
50 (if (and (procedure? f)
51 (procedure-arity-includes? f 1)
52 (list? l))
53 (let loop ([l l])
54 (cond
55 [(null? l) (void)]
56 [else (begin (f (car l)) (loop (cdr l)))]))
57 (for-each f l))]
except maybe the file heading:
2 ;; #%kernel implements `map', `for-each', `andmap', and `ormap',
3 ;; but the JIT generates faster code, especially for the
common cases.
How could I force the use of the kernel-implemented version of for-each?
2. Use DrRacket "Macro Stepper" to see exactly how the code expands. I
often just hit the "End" button, rather than stepping through. Adjusting
"Macro hiding" thing at the bottom of the window can also help.
No user macros involved in this code.
3. Look at implementation of "generator" in the Racket source code.
I've had a look at ../collects/racket/generator.rkt (assuming this is
the right place). All I can tell is that it uses continuations, as Eli said.
But the use of generator being the only difference between method a
(fast, no generator) and method b (slow, generator) it probably boils
down to "slow continuations".
Which makes me wonder if continuations are really usable in Racket (in
terms of performance)?
4. Sam's disassembler:
http://lists.racket-lang.org/dev/archive/2011-January/005321.html
I believe that's above my head, the last assembler I was fluent in was 6502.
Neil V.
Thanks for the pointers!
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