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Commit b0fe5510 authored by Ingo Molnar's avatar Ingo Molnar Committed by Sam Ravnborg
Browse files

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: default avatarIngo 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: default avatarSam 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);