On Sun, 15 Mar 2009 19:54:07 +0100, "Ingo Molnar" <mingo@xxxxxxx> said: > > * Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: > > > 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. > > doing: > > seed = (unsigned int)((now.tv_sec+1)*(now.tv_usec+1)); > > ought to settle any practical doubts. Or maybe (and I think better...) seed = (unsigned int)(now.tv_sec ^ now.tv_usec); Greetings, Alexander > Ing o :) > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" > in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > > -- 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