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| author | Ingo Molnar <mingo@elte.hu> | 2009-03-12 15:15:31 +0100 |
|---|---|---|
| committer | Sam Ravnborg <sam@ravnborg.org> | 2009-03-15 23:02:07 +0100 |
| commit | b0fe551000179c868d46266278a890eab878baca (patch) | |
| tree | 2881090d0a3da1508dc51abffe358406e0527fe1 /scripts/kconfig | |
| parent | 184832c981fd38b1052f2dfa0262e793fa6c67d3 (diff) | |
| download | kernel-crypto-b0fe551000179c868d46266278a890eab878baca.tar.gz kernel-crypto-b0fe551000179c868d46266278a890eab878baca.tar.xz kernel-crypto-b0fe551000179c868d46266278a890eab878baca.zip | |
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.c | 16 |
1 files changed, 15 insertions, 1 deletions
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 <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); |