On Fri, 2009-06-12 at 00:03 -0700, Richard Henderson wrote: > john stultz wrote: > > I suspect the alpha arch could even be further improved to provide and > > rpcc() based clocksource, but not having the hardware, I don't feel > > comfortable attempting the more complicated conversion (but I'd be glad > > to help if anyone else is interested). > > Unfortunately this isn't possible. The rpcc value is only 32-bits wide, > and so rolls over in approx 3 to 4 seconds. Thus all the contortions to > try and use the truncated value for sub 1 second adjustments. That's actually ok. The ACPI PM clocksource on x86 is only 24 bits wide and wraps every 5 seconds. The generic timekeeping code handles the wrapping and accumulation for you. > > + delta_cycles = rpcc() - state.last_time; > > + partial_tick = state.partial_tick; > > /* > > * usec = cycles * ticks_per_cycle * 2**48 * 1e6 / (2**48 * ticks) > > * = cycles * (s_t_p_c) * 1e6 / (2**48 * ticks) > > @@ -448,62 +437,9 @@ do_gettimeofday(struct timeval *tv) > > delta_usec = ((delta_usec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2; > > #endif > ... > > + return delta_usec * 1000; > > If we're going to be computing nsec now, we might as well adjust > the computation here. > > nsec = cycles * ticks_per_cycle * 1e9 / HZ > = cycles * s_t_p_c * 1e9 / (2**48 * HZ) > = cycles * s_t_p_c * 1953125 / (2**39 * HZ) > > delta_nsec = delta_cycles*state.scaled_ticks_per_cycle + partial_tick; > delta_nsec *= 1953125 > delta_nsec /= HZ << (FIX_SHIFT - 9 - 1); > delta_nsec = (delta_nsec + 1) / 2; > > As far as I can tell, the range of the dividend is about 7e17, > which still fits in an unsigned long. That seems like a good optimization, although I'm hesitant to submit anything but structural, but equivalent code changes since I don't have the hardware to test with. Might you create a patch that does this conversion and apply it on top of mine? thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
