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Message-ID: <47571B5D.5090305@iki.fi>
Date: Wed, 05 Dec 2007 23:42:53 +0200
From: Andris Pavenis <andris DOT pavenis AT iki DOT fi>
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To: djgpp-workers AT delorie DOT com
Subject: gcc-4.3. snapshots and DJGPP memory allocator efficiency
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There seem to be serious performance problems in GCC-4.3 for DJGPP due 
to slowness of free() call especially for Ada compiler.

Tried to bootstrap gcc-4.3-20071130 for DJGPP (after reverting some 
earlier changes in libiberty/configure.ac present in snapshot). 
Initially thought that compiler  (gnat1.exe) has went into some infinite 
loop when compiling gcc/ada/ali.adb for stage2.

Found that extremly long time is being spent in libibrty/hashtab.c in 
procedure htab_delete() which in that case uses free() to release 
several millions allocated memory block. htab_delete() took perhaps 
about 30 minutes on Intel Core 2 Quad 2.4GHz processor (I did not 
measure accuratelly). There is of course not much use of 4 processor 
cores as DJGPP cannot use them all.

Currently I see that perhaps the same thing happens (I haven't verified 
with debugger) when compiling gcc/ada/g-catiio.adb (killed after about 
60 minutes, I don't know how much it will still would require)

Wrote simple test (see attachment). I'm getting from this test on mostly 
idle machine (cannot get rid of WinXP though):

for s in 50000 100000 150000 200000 250000; do ./memalloctest $s; done
   50000    0.055    0.000    0.440
  100000    0.000    0.000    1.978
  150000    0.055    0.000    5.055
  200000    0.055    0.000   18.626
  250000    0.055    0.000   41.868

So one can imagine what we'll get if the number will be some millions...

Andris


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#include <algorithm>
#include <cassert>
#include <cstdlib>
#include <cstdio>
#include <ctime>

double GetTime(void)
{
  return ((double)clock()) / CLOCKS_PER_SEC;
}

void test(int size)
{
  unsigned x0 = time(NULL) | 1;
  unsigned char **foo = new unsigned char* [size];
  
  double t1 = GetTime();
  for (int i = 0; i < size; i++) {
    x0 = x0 * 65559;
    foo[i] = new unsigned char [8+x0%64];
  }

  double t2 = GetTime();
  std::random_shuffle(foo, foo+size);

  double t3 = GetTime();
  for (int i = 0; i < size; i++)
    delete [] (foo[i]);
  double t4 = GetTime();
  printf("%8d %8.3f %8.3f %8.3f \n", size, t2-t1, t3-t2, t4-t3);
  delete [] foo;
}

int main(int argc, char **argv)
{
  assert(argc == 2);
  int size = atoi(argv[1]);
  assert(size > 0);
  test(size);
  return 0;
}


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