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SubjectRe: VM: qsbench numbers
At 09.18 04/11/01 -0800, Linus Torvalds wrote:
>
>On Sun, 4 Nov 2001, Lorenzo Allegrucci wrote:
>>
>> I begin with the last Linus' kernel, three runs and kswapd CPU
>> time appended.
>
>It's interesting how your numbers decrease with more swap-space. That,
>together with the fact that the "more swap space" case also degrades the
>second time around seems to imply that we leave swap-cache pages around
>after they aren't used.
>
>Does "free" after a run has completed imply that there's still lots of
>swap used? We _should_ have gotten rid of it at "free_swap_and_cache()"
>time, but if we missed it..

lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 255984 16760 239224 0 1092 8008
-/+ buffers/cache: 7660 248324
Swap: 195512 0 195512
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
70.590u 7.640s 2:31.06 51.7% 0+0k 0+0io 19036pf+0w
lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 255984 6008 249976 0 100 1096
-/+ buffers/cache: 4812 251172
Swap: 195512 5080 190432

and with more swap..

lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 255984 13488 242496 0 532 5360
-/+ buffers/cache: 7596 248388
Swap: 390592 0 390592
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
70.180u 7.650s 2:43.22 47.6% 0+0k 0+0io 21019pf+0w
lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 255984 6596 249388 0 108 1116
-/+ buffers/cache: 5372 250612
Swap: 390592 5576 385016
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
71.030u 7.040s 2:49.45 46.0% 0+0k 0+0io 22734pf+0w
lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 255984 8808 247176 0 108 1152
-/+ buffers/cache: 7548 248436
Swap: 390592 7948 382644


>What happens if you make the "vm_swap_full()" define in <linux/swap.h> be
>unconditionally defined to "1"?

lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 256000 16772 239228 0 1104 8008
-/+ buffers/cache: 7660 248340
Swap: 195512 0 195512
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
70.530u 7.290s 2:33.26 50.7% 0+0k 0+0io 19689pf+0w
lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 256000 5132 250868 0 116 1144
-/+ buffers/cache: 3872 252128
Swap: 195512 3748 191764

..and now with 400M of swap:

lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 256000 13096 242904 0 504 4904
-/+ buffers/cache: 7688 248312
Swap: 390592 0 390592
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
70.830u 7.100s 2:29.52 52.1% 0+0k 0+0io 18488pf+0w
lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 256000 4980 251020 0 108 1132
-/+ buffers/cache: 3740 252260
Swap: 390592 3840 386752
lenstra:~/src/qsort> time ./qsbench -n 90000000 -p 1 -s 140175100
70.560u 6.840s 2:28.66 52.0% 0+0k 0+0io 18203pf+0w
lenstra:~/src/qsort> free
total used free shared buffers cached
Mem: 256000 5044 250956 0 108 1112
-/+ buffers/cache: 3824 252176
Swap: 390592 3896 386696

Performace improved and numbers stabilized.

>That should make us be more aggressive
>about freeing those swap-cache pages, and it would be interesting to see
>if it also stabilizes your numbers.
>
> Linus

I attach qsbench.c
/*
* Copyright (C) 2001 Lorenzo Allegrucci (lenstra@tiscalinet.it)
* Licensed under the GPL
*/
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

#define MAX_PROCS 1024

/**
* quick_sort - Sort in the range [l, r]
*/
void quick_sort(int a[], int l, int r)
{
int i, j, p, tmp;
int m, min, max;

i = l;
j = r;
m = (l + r) >> 1;

if (a[m] >= a[l]) {
max = a[m];
min = a[l];
} else {
max = a[l];
min = a[m];
}

if (a[r] >= max)
p = max;
else {
if (a[r] >= min)
p = a[r];
else
p = min;
}

do {
while (a[i] < p)
i++;
while (p < a[j])
j--;
if (i <= j) {
tmp = a[i];
a[i] = a[j];
a[j] = tmp;
i++;
j--;
}
} while (i <= j);

if (l < j)
quick_sort(a, l, j);
if (i < r)
quick_sort(a, i, r);
}


void do_qsort(int n, int s)
{
int * a, i, errors = 0;

if ((a = malloc(sizeof(int) * n)) == NULL) {
perror("malloc");
exit(1);
}

srand(s);
//printf("seed = %d\n", s);

for (i = 0; i < n; i++)
a[i] = rand();

quick_sort(a, 0, n - 1);

//printf("verify... "); fflush(stdout);
for (i = 0; i < n - 1; i++)
if (a[i] > a[i + 1])
errors++;
//printf("done.\n");
if (errors)
fprintf(stderr, "WARNING: %d errors.\n", errors);
free(a);
exit(0);
}


void start_procs(int n, int p, int s)
{
int i, pid[MAX_PROCS];
int status;

if (p > MAX_PROCS)
p = MAX_PROCS;

for (i = 0; i < p; i++) {
pid[i] = fork();
if (pid[i] == 0)
do_qsort(n, s);
else if (pid[i] < 0)
perror("fork");
}

for (i = 0; i < p; i++)
waitpid(pid[i], &status, 0);
}

void usage(void)
{
fprintf(stderr, "Usage: qs [-h] [-n nr_elems] [-p nr_procs]"
" [-s seed]\n");
exit(1);
}


int main(int argc, char * argv[])
{
char *n = "1000000", *p = "1", *s = "1";
int nr_elems, nr_procs, seed;
int c;

if (argc == 1)
usage();

while (1) {
c = getopt(argc, argv, "hn:p:s:V");
if (c == -1)
break;

switch (c) {
case 'h':
usage();
case 'n':
n = optarg;
break;
case 'p':
p = optarg;
break;
case 's':
s = optarg;
break;
case 'V':
printf("Version 0.93\n");
return 1;
case '?':
return 1;
}
}

nr_elems = atoi(n);
nr_procs = atoi(p);
seed = atoi(s);
start_procs(nr_elems, nr_procs, seed);

return 0;
}


--
Lorenzo
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