[racket] slow FFI?

Your test looks right, and I get similar results in Mac OS X in 64-bit
mode.

I haven't particularly tried to make foreign calls go faster, so I
expect there's room for improvement. A quick profile suggested an easy
way to trim 1/3 of the time, so I've done that (pushed to the git
repo).

In my profile, 15-20% of the time is spent in libffi's wrappers,
though, so a 5x improvement is probably an upper bound on the current
design --- leaving still a 10x difference between a direct C call and
Racket-to-C call. To do better, we might be able to use the JIT
infrastructure to generate more direct calls for simple function types,
but I'm not sure how general we can make that.

At Fri, 30 Nov 2012 10:22:08 +0000 (GMT), Denys Rtveliashvili wrote:
> Hello,
> 
> I am new to Racket. Currently I am evaluating it to find out if it works good 
> enough for my work.
> 
> One of important aspects for me is efficiency of Foreign Function Interface.
> Unfortunately, it seems that FFI is quite slow.
> 
> Please can you tell me if this is a bug in my code or FFI itself is slow? And 
> if it is indeed slow, is there a way of improving it?
> 
> Here is the code I have:
> 
> -- test.c --
> 
> void do_test(void)
> {}
> 
> -- test.rkt --
> 
> #lang racket/base
> 
> (require
>     ffi/unsafe
>     ffi/unsafe/define)
> 
> (define-ffi-definer define-t (ffi-lib "libtest"))
> 
> (define-t do_test (_fun -> _void))
> 
> (define (do_benchmark)
>     (time (for ([i (in-range 1000000)])
>         (do_test)))
> )
> 
> (for ([i (in-range 10)])
>     (do_benchmark))
> 
> -- Makefile --
> 
> libtest.so: test.o
>     gcc -fPIC -shared -pthread -o libtest.so test.o
> 
> test.o: test.c
>     gcc test.c -fPIC -shared -pthread -c -O2 -o test.o
> 
> clean:
>     rm -f test.o libtest.so
> 
> ---------
> Running the test suggests that a call to "do_test" costs about 150 nanoseconds. 
> I would expect something not larger than 5 nanoseconds. A test where C program 
> calls this function shows the call costs 3 nanoseconds.
> 
> P.S. In real life I would want to pass data to the function, most likely in 
> form of a C-structure.
> 
> P.P.S. While 150 nanoseconds may not seem like much, it easily becomes a 
> problem when many of such calls need to be done.
> 
> With kind regards,
> Denys Rtveliashvili
> Hello,
> 
> I am new to Racket. Currently I am evaluating it to find out if it works good enough for my work.
> 
> One of important aspects for me is efficiency of Foreign Function Interface.
> Unfortunately, it seems that FFI is quite slow.
> 
> Please can you tell me if this is a bug in my code or FFI itself is slow? And if it is indeed slow, is there a 
> way of improving it?
> 
> Here is the code I have:
> 
> -- test.c --
> 
> void do_test(void)
> {}
> 
> -- test.rkt --
> 
> #lang racket/base
> 
> (require
>     ffi/unsafe
>     ffi/unsafe/define)
> 
> (define-ffi-definer define-t (ffi-lib "libtest"))
> 
> (define-t do_test (_fun -> _void))
> 
> (define (do_benchmark)
>     (time (for ([i (in-range 1000000)])
>         (do_test)))
> )
> 
> (for ([i (in-range 10)])
>     (do_benchmark))
> 
> -- Makefile --
> 
> libtest.so: test.o
>     gcc -fPIC -shared -pthread -o libtest.so test.o
> 
> test.o: test.c
>     gcc test.c -fPIC -shared -pthread -c -O2 -o test.o
> 
> clean:
>     rm -f test.o libtest.so
> 
> ---------
> Running the test suggests that a call to "do_test" costs about 150 nanoseconds. I would expect 
> something not larger than 5 nanoseconds. A test where C program calls this function shows the call 
> costs 3 nanoseconds.
> 
> P.S. In real life I would want to pass data to the function, most likely in form of a C-structure.
> 
> P.P.S. While 150 nanoseconds may not seem like much, it easily becomes a problem when many of such 
> calls need to be done.
> 
> With kind regards,
> Denys Rtveliashvili
> ____________________
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