On Sun, Mar 15, 2009 at 11:53:03AM +0100, Geert Uytterhoeven wrote: > On Sun, Mar 15, 2009 at 11:28, Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: > > '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.) > > > + gettimeofday(&now, NULL); > > + > > + seed = (unsigned int)(now.tv_sec*now.tv_usec); > > Just wondering: may there be some platforms that don't offer microsecond > resolution, and tv_usec is always zero? That would indeed be bad for the seed. Googling did not turn up anything. Sam -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
