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authorIngo Molnar <mingo@elte.hu>2009-03-12 15:15:31 +0100
committerSam Ravnborg <sam@ravnborg.org>2009-03-15 23:02:07 +0100
commitb0fe551000179c868d46266278a890eab878baca (patch)
tree2881090d0a3da1508dc51abffe358406e0527fe1 /scripts/kconfig
parent184832c981fd38b1052f2dfa0262e793fa6c67d3 (diff)
kconfig: improve seed in randconfig
'make randconfig' uses glibc's rand function, and the seed of that PRNG is set via: srand(time(NULL)); But 'time()' only increases once every second - freezing the randconfig result within a single second. My Nehalem testbox does randconfig much faster than 1 second and i have a few scripts that do 'randconfig until condition X' loops. Those scripts currently waste a lot of CPU time due to randconfig changing its seed only once per second currently. Change the seed to be micrseconds based. (I checked the statistical spread of the seed - the now.tv_sec*now.tv_usec multiplication there further improves it.) Signed-off-by: Ingo Molnar <mingo@elte.hu> Cc: Roman Zippel <zippel@linux-m68k.org> [sam: fix for systems where usec is zero - noticed by Geert Uytterhoeven] Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Diffstat (limited to 'scripts/kconfig')
-rw-r--r--scripts/kconfig/conf.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
index 3e1057f885c6..d190092c3b6e 100644
--- a/scripts/kconfig/conf.c
+++ b/scripts/kconfig/conf.c
@@ -11,6 +11,7 @@
#include <time.h>
#include <unistd.h>
#include <sys/stat.h>
+#include <sys/time.h>
#define LKC_DIRECT_LINK
#include "lkc.h"
@@ -464,9 +465,22 @@ int main(int ac, char **av)
input_mode = set_yes;
break;
case 'r':
+ {
+ struct timeval now;
+ unsigned int seed;
+
+ /*
+ * Use microseconds derived seed,
+ * compensate for systems where it may be zero
+ */
+ gettimeofday(&now, NULL);
+
+ seed = (unsigned int)((now.tv_sec + 1) * (now.tv_usec + 1));
+ srand(seed);
+
input_mode = set_random;
- srand(time(NULL));
break;
+ }
case 'h':
printf(_("See README for usage info\n"));
exit(0);

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