Re: [RFC] temporary Lisp_Strings

[Dmitry Antipov <dmantipov@yandex.ru>]

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On 09/02/2014 06:00 PM, Stefan Monnier wrote:

> Have you made some preliminary measurements (on microbenchmarks) to try
> and see how much speed up we might gain?  Given the cost of strlen and
> parse_str_as_multibyte, I'd expect that the best-case benefit might turn
> out to be rather small.

For the moment, I don't have an idea how to benchmark parse_str_as_multibyte
in "near-to-real-use" conditions.  But I guess that we can have some gain
for "simple" (short, especially short unibyte) strings. That guess is based
on the following results (note ~3x speedup in strcpy/strcat workload):

$ gcc -Wall -O2 -o t-alloca t-alloca.c t-use.c
$
$ /usr/bin/time ./t-alloca 100 100
Use malloc for allocation and sprintf for workload
2.23user 0.00system 0:02.23elapsed 100%CPU (0avgtext+0avgdata 1440maxresident)k
0inputs+0outputs (0major+59minor)pagefaults 0swaps
$
$ /usr/bin/time ./t-alloca 100 100 x
Use alloca for allocation and sprintf for workload
1.85user 0.00system 0:01.85elapsed 99%CPU (0avgtext+0avgdata 1436maxresident)k
0inputs+0outputs (0major+59minor)pagefaults 0swaps
$
$ gcc -DFAST -Wall -O2 -o t-alloca t-alloca.c t-use.c
$
$ /usr/bin/time ./t-alloca 100 100
Use malloc for allocation and strcpy/strcat for workload
0.56user 0.00system 0:00.56elapsed 99%CPU (0avgtext+0avgdata 1440maxresident)k
0inputs+0outputs (0major+59minor)pagefaults 0swaps
$
$ /usr/bin/time ./t-alloca 100 100 x
Use alloca for allocation and strcpy/strcat for workload
0.20user 0.00system 0:00.20elapsed 100%CPU (0avgtext+0avgdata 1440maxresident)k
0inputs+0outputs (0major+60minor)pagefaults 0swaps

Dmitry


[-- Attachment #2: t-alloca.c --]
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef FAST
#define FUNCNAME "strcpy/strcat"
#else
#define FUNCNAME "sprintf"
#endif

extern void use_with_malloc (char *, int, char *, int);
extern void use_with_alloca (char *, int, char *, int);

int
main (int argc, char *argv[])
{
  char *p1, *p2;
  int i, len1, len2;

  if (argc >= 3)
    {
      len1 = atoi (argv[1]);
      len2 = atoi (argv[2]);

      p1 = malloc (len1 + 1);
      memset (p1, 'a', len1);
      p1[len1] = '\0';

      p2 = malloc (len2 + 1);
      memset (p1, 'b', len2);
      p2[len2] = '\0';

      printf ("Use %s for allocation and %s for workload\n",
	      (argc == 3) ? "malloc" : "alloca", FUNCNAME);

      for (i = 0; i < 10000000; i++)
	{
	  if (argc == 3)
	    use_with_malloc (p1, len1, p2, len2);
	  else
	    use_with_alloca (p1, len1, p2, len2);
	}
    }
  return 0;
}

[-- Attachment #3: t-use.c --]
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *ptr;

void
use_with_malloc (char *p, int plen, char *q, int qlen)
{
  ptr = malloc (plen + qlen + 1);
#ifdef FAST
  strcpy (ptr, p);
  strcat (ptr, q);
#else
  sprintf (ptr, "%s%s", p, q);
#endif
  (void) ptr;
  free (ptr);
}

void
use_with_alloca (char *p, int plen, char *q, int qlen)
{
  ptr = alloca (plen + qlen + 1);
#ifdef FAST
  strcpy (ptr, p);
  strcat (ptr, q);
#else
  sprintf (ptr, "%s%s", p, q);
#endif
  (void) ptr;
}