On Friday 04 May 2007 18:52, Ingo Molnar wrote:
> agreed. Con, IIRC you wrote a testcase for this, right? Could you please
> send us the results of that testing?
Yes, sorry it's a crappy test app but works on 32bit. Timed with prefetch
disabled and then enabled swap prefetch saves ~5 seconds on average hardware
on this one test case. I had many users try this and the results were between
2 and 10 seconds, but always showed a saving on this testcase. This effect
easily occurs on printing a big picture, editing a large file, compressing an
iso image or whatever in real world workloads. Smaller, but much more
frequent effects of this over the course of a day obviously also occur and do
add up.
--
-ck
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <time.h>
void fatal(const char *format, ...)
{
va_list ap;
if (format) {
va_start(ap, format);
vfprintf(stderr, format, ap);
va_end(ap);
}
fprintf(stderr, "Fatal error - exiting\n");
exit(1);
}
size_t get_ram(void)
{
unsigned long ramsize;
FILE *meminfo;
char aux[256];
if(!(meminfo = fopen("/proc/meminfo", "r")))
fatal("fopen\n");
while( !feof(meminfo) && !fscanf(meminfo, "MemTotal: %lu kB", &ramsize) )
fgets(aux,sizeof(aux),meminfo);
if (fclose(meminfo) == -1)
fatal("fclose");
return ramsize * 1000;
}
unsigned long get_usecs(struct timespec *myts)
{
if (clock_gettime(CLOCK_REALTIME, myts))
fatal("clock_gettime");
return (myts->tv_sec * 1000000 + myts->tv_nsec / 1000 );
}
int main(void)
{
unsigned long current_time, time_diff;
struct timespec myts;
char *buf1, *buf2, *buf3, *buf4;
size_t size, full_size = get_ram();
int sleep_seconds = 600;
size = full_size * 7 / 10;
printf("Starting first malloc of %d bytes\n", size);
buf1 = malloc(size);
if (buf1 == (char *)-1)
fatal("Failed to malloc 1st buffer\n");
memset(buf1, 0, size);
printf("Completed first malloc and starting second malloc of %d bytes\n", full_size);
buf2 = malloc(full_size);
if (buf2 == (char *)-1)
fatal("Failed to malloc 2nd buffer\n");
memset(buf2, 0, full_size);
buf4 = malloc(1);
for (buf3 = buf2 + full_size; buf3 > buf2; buf3--)
*buf4 = *buf3;
free(buf2);
printf("Completed second malloc and free\n");
printf("Sleeping for %d seconds\n", sleep_seconds);
sleep(sleep_seconds);
printf("Important part - starting read of first malloc\n");
time_diff = current_time = get_usecs(&myts);
for (buf3 = buf1; buf3 < buf1 + size; buf3++)
*buf4 = *buf3;
current_time = get_usecs(&myts);
free(buf4);
free(buf1);
printf("Completed read and freeing of first malloc\n");
time_diff = current_time - time_diff;
printf("Timed portion %lu microseconds\n",time_diff);
return 0;
}
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