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SubjectRe: [PATCH v4 4/4] timekeeping: utilize the suspend-nonstop clocksource to count suspended time
On 03/11/2013 08:56 PM, Feng Tang wrote:
> + /*
> + * After system resumes, we need to calculate the suspended time and
> + * compensate it for the OS time. There are 3 sources that could be
> + * used: Nonstop clocksource during suspend, persistent clock and rtc
> + * device.
> + *
> + * One specific platform may have 1 or 2 or all of them, and the
> + * preference will be:
> + * suspend-nonstop clocksource -> persistent clock -> rtc
> + * The less preferred source will only be tried if there is no better
> + * usable source. The rtc part is handled separately in rtc core code.
> + */
> + cycle_now = clock->read(clock);
> + if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
> + cycle_now > clock->cycle_last) {
> + u64 num, max = ULLONG_MAX;
> + u32 mult = clock->mult;
> + u32 shift = clock->shift;
> + s64 nsec = 0;
> +
> + cycle_delta = (cycle_now - clock->cycle_last) & clock->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;
> +
> + ts_delta = ns_to_timespec(nsec);
> + suspendtime_found = true;
> + } else if (timespec_compare(&ts_new, &timekeeping_suspend_time) > 0) {
> + ts_delta = timespec_sub(ts_new, timekeeping_suspend_time);
> + suspendtime_found = true;
> }
> - /* re-base the last cycle value */
> - tk->clock->cycle_last = tk->clock->read(tk->clock);
> +
> + if (suspendtime_found)
> + __timekeeping_inject_sleeptime(tk, &ts_delta);
> +
> + /* Re-base the last cycle value */
> + clock->cycle_last = clock->read(clock);
It seems like since we unconditionally read the clock above, this last
line could be reworked to be:
clock->cycle_last = cycle_now;

Which would save re-reading the clocksource.

If you don't have any objections I'll fold that small change into your
patch.

thanks
-john



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