Re: [patch 4/6] timekeeping: Use mul_u64_u32_shr() instead of open coding it

David Gibson
2016-12-08T23:47:45Z

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On Thu, Dec 08, 2016 at 08:49:38PM -0000, Thomas Gleixner wrote:
> The resume code must deal with a clocksource delta which is potentially big
> enough to overflow the 64bit mult.
>
> Replace the open coded handling with the proper function.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> kernel/time/timekeeping.c | 26 +++++---------------------
> 1 file changed, 5 insertions(+), 21 deletions(-)
>
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1615,7 +1615,7 @@ void timekeeping_resume(void)
> struct clocksource *clock = tk->tkr_mono.clock;
> unsigned long flags;
> struct timespec64 ts_new, ts_delta;
> - cycle_t cycle_now, cycle_delta;
> + cycle_t cycle_now;
>
> sleeptime_injected = false;
> read_persistent_clock64(&ts_new);
> @@ -1641,27 +1641,11 @@ void timekeeping_resume(void)
> cycle_now = tk->tkr_mono.read(clock);
> if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
> cycle_now > tk->tkr_mono.cycle_last) {
> - u64 num, max = ULLONG_MAX;
> - u32 mult = clock->mult;
> - u32 shift = clock->shift;
> - s64 nsec = 0;
> -
> - cycle_delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last,
> - tk->tkr_mono.mask);
> -
> - /*
> - * "cycle_delta * mutl" may cause 64 bits overflow, if the
> - * suspended time is too long. In that case we need do the
> - * 64 bits math carefully
> - */
> - do_div(max, mult);
> - if (cycle_delta > max) {
> - num = div64_u64(cycle_delta, max);
> - nsec = (((u64) max * mult) >> shift) * num;
> - cycle_delta -= num * max;
> - }
> - nsec += ((u64) cycle_delta * mult) >> shift;
> + u64 nsec, cyc_delta;
>
> + cyc_delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last,
> + tk->tkr_mono.mask);
> + nsec = mul_u64_u32_shr(cyc_delta, clock->mult, clock->shift);
> ts_delta = ns_to_timespec64(nsec);
> sleeptime_injected = true;
> } else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
>
>

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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