On Friday, June 24, 2016 9:31:35 PM CEST Shreyas B Prabhu wrote:
quoted
If those functions are called less often than cpuidle_enter_state(),
we could just move the division there. Since the divisor is constant,
do_div() can convert it into a multiply and shift, or we could use
your the code you suggest above, or use a 32-bit division most of
the time:
if (diff <= UINT_MAX)
diff_32 = (u32)diff / NSECS_PER_USEC;
else
diff_32 = div_u64(diff, NSECS_PER_USEC;
which gcc itself will turn into a multiplication or series of
shifts on CPUs on which that is faster.
I'm not sure which division method of the three suggested here to use.
Does anyone have a strong preference?
It depends on how accurate we want it and how long we expect
the times to be. The optimization for the 4.2 second cutoff
for doing a 32-bit division only makes sense if the majority
of the sleep times are below that.
Arnd