On Mon, 21 Feb 2011, Arnd Bergmann wrote: > On Monday 21 February 2011, Russell King - ARM Linux wrote: > > Eg, LOW_RES_NSEC is exported to userspace via the posix clocks interface. > > > > NSEC_PER_SEC and TICK_NSEC are used for cmos clock updates, so probably > > don't matter too much there. TICK_NSEC is also used by the scheduler, > > time conversions (timespec/timeval to/from jiffies) and profiling code. > > > > NSEC_PER_JIFFY is used by the jiffy clocksource code, which only matters > > if you don't have your own clocksource. > > > > So, I feel very uneasy about saying that CLOCK_TICK_RATE doesn't matter > > anymore given all the places which reference something that's derived > > from it. > > All the calculations based off of CLOCK_TICK_RATE are derived from ACTHZ, > which is either the correct value based on the underlying HW timer tick, > or slightly off, when either the HW tick or the value of CLOCK_TICK_RATE > is not a true multiple of HZ. > > In fact, I'm pretty sure that it's off on a lot of machines: > > arch/frv/include/asm/timex.h:#define CLOCK_TICK_RATE 1193180 /* Underlying HZ */ > arch/m68k/include/asm/timex.h:#define CLOCK_TICK_RATE 1193180 /* Underlying HZ */ > arch/mips/include/asm/timex.h:#define CLOCK_TICK_RATE 1193182 > arch/parisc/include/asm/timex.h:#define CLOCK_TICK_RATE 1193180 /* Underlying HZ */ > arch/s390/include/asm/timex.h:#define CLOCK_TICK_RATE 1193180 /* Underlying HZ */ > arch/sh/include/asm/timex.h:#define CLOCK_TICK_RATE 1193180 > arch/x86/include/asm/timex.h:#define CLOCK_TICK_RATE PIT_TICK_RATE > arch/xtensa/include/asm/timex.h:#define CLOCK_TICK_RATE 1193180 /* (everyone is using this value) */ > > None of these is actually using a PC-style PIT these days, the just copied the > definition blindly from old i386. I think a simple > > #define ACTHZ (HZ << 8) > > would fix more than it can break, and most likely nobody would ever notice > the difference. If we do that, CLOCK_TICK_RATE becomes unused. Indeed. tglx -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
