Re: [Haskell-cafe] ANNOUNCE: cinvoke 0.1 released

On Wed, Mar 09, 2011 at 05:50:12PM +0100, Gábor Lehel wrote:

On Wed, Mar 9, 2011 at 5:26 PM, Remi Turk wrote:

...

Count on it having at least an order of magnitude more overhead. I did some simple test of calling the following three trivial functions (with constant arguments, and ignoring the return values, 2M times) and got the following timings:

 int blub0() { return 42; }  int blub1(int a) { return 42; }  int blub5(int a, int b, int c, int d, int e) { return 42; }

       Unsafe FFI   Safe FFI   Safe dynamic FFI   CInvoke blub0   0.03         0.19       0.20               1.62 blub1   0.03         0.20       0.20               2.44 blub5   0.04         0.20       0.20               4.35

It's not that bad for functions that actually (try to) do something though. For example, trying to remove a non-existent file:

unlink  3.06         3.04       3.27               7.15

If I remember correctly, libffi was slightly faster, but mostly thanks to the fact that I didn't make it exception safe yet.

So if you care about performance and are able to directly use the FFI, you clearly should.

That describes my situation. Thanks!

For the record, what units were your measurements in?

(I notice that the overhead of safe FFI calls seems to be pretty smallish, which is also quite heartening.)

Everything is in seconds. So for example, 2 million unsafe calls to blub0 take 0.03 seconds: ~15ns or ~42 cycles per call (including replicateM_ overhead). I just noticed in my little non-scientific benchmark that the overhead for safe calls is significantly higher when compiling with -threaded:       Unsafe FFI   Safe FFI   Safe dynamic FFI   CInvoke blub0 0.04 0.36 0.35 2.27 blub1 0.05 0.36 0.36 3.52 blub5 0.05 0.37 0.37 5.72 unlink 3.26 3.21 3.56 8.41 Groeten, Remi