Commit b0fe5510 authored Mar 12, 2009 by Ingo Molnar Committed by Sam Ravnborg Mar 15, 2009

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>

parent 184832c9

scripts/kconfig/conf.c

+15 −1

Original line number	Diff line number	Diff line
		@@ -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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