'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@xxxxxxx>
Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
---
scripts/kconfig/conf.c | 15 ++++++++++++++-
1 files changed, 14 insertions(+), 1 deletions(-)
diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
index 3e1057f..4f1b488 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 +465,21 @@ int main(int ac, char **av)
input_mode = set_yes;
break;
case 'r':
+ {
+ struct timeval now;
+ unsigned int seed;
+
+ /*
+ * Use microseconds derived seed:
+ */
+ gettimeofday(&now, NULL);
+
+ seed = (unsigned int)(now.tv_sec*now.tv_usec);
+ srand(seed);
+
input_mode = set_random;
- srand(time(NULL));
break;
+ }
case 'h':
printf(_("See README for usage info\n"));
exit(0);
--
1.6.0.2.GIT
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