Python is darn fast (was: How fast is Python)

[Michele Simionato]

I posted this few weeks ago (remember the C Sharp thread?) but it went
unnoticed on the large mass of posts, so let me retry. Here I get Python+
Psyco twice as fast as optimized C, so I would like to now if something
is wrong on my old laptop and if anybody can reproduce my results.
Here are I my numbers for calling the error function a million times
(Python 2.3, Psyco 1.0, Red Hat Linux 7.3, Pentium II 366 MHz):

$ time p23 erf.py
real 0m0.614s
user 0m0.551s
sys 0m0.029s

This is twice as fast as optimized C:

$ gcc erf.c -lm -o3
$ time ./a.out
real 0m1.125s
user 0m1.086s
sys 0m0.006s

Here is the situation for pure Python

$time p23 erf.jy
real 0m25.761s
user 0m25.012s
sys 0m0.049s

and, just for fun, here is Jython performance:

$ time jython erf.jy
real 0m42.979s
user 0m41.430s
sys 0m0.361s

The source code follows (copied from Alex Martelli's post):

----------------------------------------------------------------------

$ cat erf.py
import math
import psyco
psyco.full()

def erfc(x):
exp = math.exp

p = 0.3275911
a1 = 0.254829592
a2 = -0.284496736
a3 = 1.421413741
a4 = -1.453152027
a5 = 1.061405429

t = 1.0 / (1.0 + p*x)
erfcx = ( (a1 + (a2 + (a3 +
(a4 + a5*t)*t)*t)*t)* t ) * exp(-x*x)
return erfcx

def main():
erg = 0.0

for i in xrange(1000000) :
erg += erfc(0.456)

if __name__ == '__main__':
main()

--------------------------------------------------------------------------

# python/jython version = same without "import psyco; psyco.full()"

--------------------------------------------------------------------------

$cat erf.c
#include <stdio.h>
#include <math.h>

double erfc( double x )
{
double p, a1, a2, a3, a4, a5;
double t, erfcx;

p = 0.3275911;
a1 = 0.254829592;
a2 = -0.284496736;
a3 = 1.421413741;
a4 = -1.453152027;
a5 = 1.061405429;

t = 1.0 / (1.0 + p*x);
erfcx = ( (a1 + (a2 + (a3 +
(a4 + a5*t)*t)*t)*t)* t ) * exp(-x*x);

return erfcx;
}

int main()
{
double erg=0.0;
int i;

for(i=0; i<1000000; i++)
{
erg = erg + erfc(0.456);
}

return 0;
}

Michele Simionato, Ph. D.
Mi************* *@libero.it
http://www.phyast.pitt.edu/~micheles
--- Currently looking for a job ---

[Irmen de Jong]

Michele Simionato wrote:

I posted this few weeks ago (remember the C Sharp thread?) but it went
unnoticed on the large mass of posts, so let me retry. Here I get Python+
Psyco twice as fast as optimized C, so I would like to now if something
is wrong on my old laptop and if anybody can reproduce my results.

I can. :-)

I had to increase the loop counter by a factor of 10 because it
ran too fast on my machine (celeron 533 mhz), and added a print statement
of the accumulated sum (erg). These are my results:

[irmen@atlantis]$ gcc -O3 -march=pentium2 -mcpu=pentium2 -lm erf.c

[irmen@atlantis]$ time ./a.out
5190039.338694
4.11user 0.00system 0:04.11elapsed 99%CPU (0avgtext+0avgd ata 0maxresident)k
0inputs+0output s (103major+13min or)pagefaults 0swaps

[irmen@atlantis]$ time python2.3 erf.py
5190039.33869
2.91user 0.01system 0:02.92elapsed 99%CPU (0avgtext+0avgd ata 0maxresident)k
0inputs+0output s (544major+380mi nor)pagefaults 0swaps

This is with gcc 3.2.2 on Mandrake 9.1.

While Python + Psyco is not twice as fast as compiled & optimized C,
it's still faster by almost 30% on my system, which is still great!!

--Irmen

[Irmen de Jong]

Michele Simionato wrote:

I posted this few weeks ago (remember the C Sharp thread?) but it went
unnoticed on the large mass of posts, so let me retry. Here I get Python+
Psyco twice as fast as optimized C, so I would like to now if something
is wrong on my old laptop and if anybody can reproduce my results.

I can. :-)

I had to increase the loop counter by a factor of 10 because it
ran too fast on my machine (celeron 533 mhz), and added a print statement
of the accumulated sum (erg). These are my results:

[irmen@atlantis]$ gcc -O3 -march=pentium2 -mcpu=pentium2 -lm erf.c

[irmen@atlantis]$ time ./a.out
5190039.338694
4.11user 0.00system 0:04.11elapsed 99%CPU (0avgtext+0avgd ata 0maxresident)k
0inputs+0output s (103major+13min or)pagefaults 0swaps

[irmen@atlantis]$ time python2.3 erf.py
5190039.33869
2.91user 0.01system 0:02.92elapsed 99%CPU (0avgtext+0avgd ata 0maxresident)k
0inputs+0output s (544major+380mi nor)pagefaults 0swaps

This is with gcc 3.2.2 on Mandrake 9.1.

While Python + Psyco is not twice as fast as compiled & optimized C,
it's still faster by almost 30% on my system, which is still great!!

--Irmen

[Lawrence Oluyede]

Michele Simionato wrote:

$ time p23 erf.py
real 0m0.614s
user 0m0.551s
sys 0m0.029s

This is twice as fast as optimized C:

$ gcc erf.c -lm -o3
$ time ./a.out
real 0m1.125s
user 0m1.086s
sys 0m0.006s

Here is the situation for pure Python

$time p23 erf.jy
real 0m25.761s
user 0m25.012s
sys 0m0.049s

and, just for fun, here is Jython performance:

$ time jython erf.jy
real 0m42.979s
user 0m41.430s
sys 0m0.361s

Mmm...on my machine C is faster. What version of GCC do you have? I think
2.9x, right?

These are my timings (Debian GNU Linux Unstable, Duron 1300, Python2.3,
Psyco CVS, GCC 3.3.2, Java 1.4.1):

$ time python erf.py

real 0m0.251s
user 0m0.207s
sys 0m0.012s

$ gcc erf.c -lm -O3
$ time ./a.out

real 0m0.162s
user 0m0.157s
sys 0m0.001s

Notice that C is faster than Psyco + Python2.3 on my machine (about 65% of
speedup)

Without Psyco Python2.3 tooks about 6 seconds

$ time python erf.jy

real 0m6.177s
user 0m6.040s
sys 0m0.010s
And Jython is definitely slower :)

$ time jython erf.jy

real 0m10.423s
user 0m9.506s
sys 0m0.197s
--
Lawrence "Rhymes" Oluyede
http://loluyede.blogspot.com
rh****@NOSPAMmy self.com

[Lawrence Oluyede]

Michele Simionato wrote:

$ time p23 erf.py
real 0m0.614s
user 0m0.551s
sys 0m0.029s

This is twice as fast as optimized C:

$ gcc erf.c -lm -o3
$ time ./a.out
real 0m1.125s
user 0m1.086s
sys 0m0.006s

Here is the situation for pure Python

$time p23 erf.jy
real 0m25.761s
user 0m25.012s
sys 0m0.049s

and, just for fun, here is Jython performance:

$ time jython erf.jy
real 0m42.979s
user 0m41.430s
sys 0m0.361s

Mmm...on my machine C is faster. What version of GCC do you have? I think
2.9x, right?

These are my timings (Debian GNU Linux Unstable, Duron 1300, Python2.3,
Psyco CVS, GCC 3.3.2, Java 1.4.1):

$ time python erf.py

real 0m0.251s
user 0m0.207s
sys 0m0.012s

$ gcc erf.c -lm -O3
$ time ./a.out

real 0m0.162s
user 0m0.157s
sys 0m0.001s

Notice that C is faster than Psyco + Python2.3 on my machine (about 65% of
speedup)

Without Psyco Python2.3 tooks about 6 seconds

$ time python erf.jy

real 0m6.177s
user 0m6.040s
sys 0m0.010s
And Jython is definitely slower :)

$ time jython erf.jy

real 0m10.423s
user 0m9.506s
sys 0m0.197s
--
Lawrence "Rhymes" Oluyede
http://loluyede.blogspot.com
rh****@NOSPAMmy self.com

[P]

Michele Simionato wrote:

I posted this few weeks ago (remember the C Sharp thread?) but it went
unnoticed on the large mass of posts, so let me retry. Here I get Python+
Psyco twice as fast as optimized C

$ gcc erf.c -lm -O3

try a 3.x series gcc with the appropriate -march=pentium3
You'll be pleasently surprised. I can't understand how
the sudden improvment of gcc code generation lately hasn't
been hyped more? If you want to try different machines
then http://www.pixelbeat.org/scripts/gcccpuopt will give
you the appropriate machine specific gcc options to use.
Note also -ffast-math might help a lot in this application?

cheers,
Pádraig.

[P]

Michele Simionato wrote:

I posted this few weeks ago (remember the C Sharp thread?) but it went
unnoticed on the large mass of posts, so let me retry. Here I get Python+
Psyco twice as fast as optimized C

$ gcc erf.c -lm -O3

try a 3.x series gcc with the appropriate -march=pentium3
You'll be pleasently surprised. I can't understand how
the sudden improvment of gcc code generation lately hasn't
been hyped more? If you want to try different machines
then http://www.pixelbeat.org/scripts/gcccpuopt will give
you the appropriate machine specific gcc options to use.
Note also -ffast-math might help a lot in this application?

cheers,
Pádraig.

[John J. Lee]

Irmen de Jong <[e-mail]> writes:

[e-mail] m wrote:

try a 3.x series gcc with the appropriate -march=pentium3
You'll be pleasently surprised.

In my other reply I mentioned that I still get a Python+Psyco
advantage of 30% over a gcc 3.2.2 compiled version.
My gcc is doing a lot better than Michele's reported 50% difference,
but Python+Psyco still wins :-)

So, the interesting part is: why?
John

[John J. Lee]

Irmen de Jong <[e-mail]> writes:

[e-mail] m wrote:

try a 3.x series gcc with the appropriate -march=pentium3
You'll be pleasently surprised.

In my other reply I mentioned that I still get a Python+Psyco
advantage of 30% over a gcc 3.2.2 compiled version.
My gcc is doing a lot better than Michele's reported 50% difference,
but Python+Psyco still wins :-)

So, the interesting part is: why?
John

[Simon Burton]

On Sun, 24 Aug 2003 00:31:15 +0100, John J. Lee wrote:

Irmen de Jong <[e-mail]> writes:

[e-mail] m wrote:
.... but Python+Psyco still wins :-)

So, the interesting part is: why?
John

My suspicion is that when psyco looks at erfc, it
finds that nothing changes and so replaces the
function call with the resulting number (am i right? it's the
same each time?). This is what a "specializi ng compiler"
would do, me thinks. So, try using a different number
with each call.

Simon.