On 07/18, Oleg Nesterov wrote:
>
> + * NOTE! currently the only user is cputime_adjust() and thus
> + *
> + * stime < total && rtime > total
> + *
> + * this means that the end result is always precise and the additional
> + * div64_u64_rem() inside the main loop is called at most once.
Ah, I just noticed that the comment is not 100% correct... in theory we
can drop the precision and even do div64_u64_rem() more than once, but this
can only happen if stime or total = stime + utime is "really" huge, I don't
think this can happen in practice...
We can probably just do
static u64 scale_stime(u64 stime, u64 rtime, u64 total)
{
u64 res = 0, div, rem;
if (ilog2(stime) + ilog2(rtime) > 62) {
div = div64_u64_rem(rtime, total, &rem);
res += div * stime;
rtime = rem;
int shift = ilog2(stime) + ilog2(rtime) - 62;
if (shift > 0) {
rtime >>= shift;
total >>= shitt;
if (!total)
return res;
}
}
return res + div64_u64(stime * rtime, total);
}
but this way the code looks less generic.
Oleg.
