From b0fe551000179c868d46266278a890eab878baca Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Thu, 12 Mar 2009 15:15:31 +0100 Subject: [PATCH] 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 Cc: Roman Zippel [sam: fix for systems where usec is zero - noticed by Geert Uytterhoeven] Signed-off-by: Sam Ravnborg --- scripts/kconfig/conf.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c index 3e1057f885c..d190092c3b6 100644 --- a/scripts/kconfig/conf.c +++ b/scripts/kconfig/conf.c @@ -11,6 +11,7 @@ #include #include #include +#include #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); -- 2.41.1