From: Ingo Molnar <mingo@elte.hu>
Date: Thu, 12 Mar 2009 14:15:31 +0000 (+0100)
Subject: kconfig: improve seed in randconfig
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=b0fe551000179c868d46266278a890eab878baca;p=linux-beck.git

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>
---

diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
index 3e1057f885c6..d190092c3b6e 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);