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.
+ 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.
r~
--
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
