On Fri, Nov 27, 2015 at 11:49:40AM +0100, Paolo Bonzini wrote:
[ sorry missed your message on Friday, replying now ]
> On 27/11/2015 09:12, Roman Kagan wrote:
> >> > + n = div64_u64(time_now - stimer->exp_time, stimer->count) + 1;
> >> > + stimer->exp_time += n * stimer->count;
> > This is actually just a reminder calculation so I'd rather do it
> > directly with div64_u64_rem().
>
> It took me a while to understand why it was a remained. :)
It gets easier if you think of it this way: we've slipped a few whole
periods and the remainder of the slack into the current period, so
the time left till the next tick is ("count" is the timer period here)
delta = count - slack % count
where
slack = time_now - exp_time
This gives you immediately your
> exp_time = time_now + (count - (time_now - exp_time) % count)
Roman.
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