Bug#572746: libm: sinf/cosf performance is awful on amd64

[Jerome Vizcaino <vizcaino_jerome@yahoo.fr>]

Package: libc6
Version: 2.10.2-6
Severity: normal

Hi,

After many tests and research I've come to the conclusion that the float variants 
of
sin/cos (and maybe others) are anormaly slow Debian amd64.
The performance loss is really impressive (around 8 to 9 times slower).
I've attached the prog used to make my experiments and used it in the following 
cases.

+ Lenny-amd64: sinf/cosf is really slow
+ Lenny-i386: float performance is ok (faster than the cos/sin using double)
+ Sid-amd64: sinf/cosf slow
+ Lenny-amd64 using lenny-i386 binary and 32bits libs: float performance is OK.

+ OpenSuse 64 bits (10.3 and 11.1): using the binary compiled on lenny-amd64, 
the tests run fine !
=> The problem is not compiler related.

There seems to be a problem with the way libm is compiled for the amd64 
architecture on Debian.
This is why the OpenSuse test was run: the problem is somewhere in the compile 
chain or debian specific patches.

We're extensively using these for calculations and this is a real problem. Using 
cos/sin as
a temporary workaround would do the trick but this is still slower than the 
sinf/cosf 
implementations that works so well on 32 bits computers...

Thank you

Jerome

-- System Information:
Debian Release: squeeze/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.32-trunk-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8) (ignored: LC_ALL 
set to en_US.utf8)
Shell: /bin/sh linked to /bin/bash

Versions of packages libc6 depends on:
ii  libc-bin                      2.10.2-6   Embedded GNU C Library: Binaries
ii  libgcc1                       1:4.4.3-3  GCC support library

libc6 recommends no packages.

Versions of packages libc6 suggests:
ii  debconf [debconf-2.0]         1.5.28     Debian configuration management sy
pn  glibc-doc                     <none>     (no description available)
ii  locales                       2.10.2-6   Embedded GNU C Library: National L

-- debconf information excluded

CC=gcc
CFLAGS=-DNDEBUG -O3 -D_ISOC99_SOURCE -Wall -Wextra
LDFLAGS=-lm

all: test_trig

clean:
	rm test_trig

test_trig: test_trig.c

#include <math.h>
#include <sys/time.h>
#include <stdio.h>




int main(void) 
{
  const int nbElement_i = 10000000;
  int i=0;
  float f1=0.0f, f2=0.0f, f3=0.0f;
  
  struct timeval tv1, tv2; 

  printf("Testing %d sinf and cosf... ", nbElement_i);
  fflush(stdout);
  
  gettimeofday(&tv1, NULL);

  for(i=0; i<nbElement_i; i++){
    f1 += cosf(i); 
    f2 += sinf(i);
  }

  // This is needed for gcc to know a and b results
  // really matters, otherwise sin and cos could
  // be ignored.
  f3 = f1+f2; 

  gettimeofday(&tv2, NULL);

  //
  printf("Result: %f, Duration: %ld sec %ld usec\n", f3, tv2.tv_sec - tv1.tv_sec, tv2.tv_usec - tv1.tv_usec);

  f1 = 0.0f; f2 = 0.0f;
  printf("Testing %d sin and cos (with float args)... ", nbElement_i);
  fflush(stdout);
  
  gettimeofday(&tv1, NULL);

  for(i=0; i<nbElement_i; i++){
    f1 += cos(i); 
    f2 += sin(i);
  }

  // This is needed for gcc to know a and b results
  // really matters, otherwise sin and cos could
  // be ignored.
  f3 = f1+f2; 

  gettimeofday(&tv2, NULL);

  //
  printf("Result: %f, Duration: %ld sec %ld usec\n", f3, tv2.tv_sec - tv1.tv_sec, tv2.tv_usec - tv1.tv_usec);
  
  return 0;
}