On Wed, Mar 06, 2013 at 03:15:49PM +0100, Thomas Gleixner wrote:
> On Wed, 6 Mar 2013, Feng Tang wrote:
>
> > There are some new processors whose TSC clocksource won't stop during
> > suspend. Currently, after system resumes, kernel will use persistent
> > clock or RTC to compensate the sleep time, but for those new types of
> > clocksources, we could skip the special compensation from external
> > sources, and just use current clocksource for time recounting.
> >
> > This can solve some time drift bugs caused by some not-so-accurate or
> > error-prone RTC devices.
> >
> > The current way to count suspened time is first try to use the persistent
> > clock, and then try the rtc if persistent clock can't be used. This
> > patch will change the trying order to:
> > suspend-nonstop clocksource -> persistent clock -> rtc
> >
> > Signed-off-by: Feng Tang <feng.t...@intel.com>
> > ---
> > kernel/time/timekeeping.c | 42 ++++++++++++++++++++++++++++++++++--------
> > 1 file changed, 34 insertions(+), 8 deletions(-)
> > - read_persistent_clock(&ts);
> > + ts_delta.tv_sec = 0;
> > + read_persistent_clock(&ts_new);
> >
> > clockevents_resume();
> > clocksource_resume();
> >
> > write_seqlock_irqsave(&tk->lock, flags);
> >
> > - if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
> > - ts = timespec_sub(ts, timekeeping_suspend_time);
> > - __timekeeping_inject_sleeptime(tk, &ts);
> > - }
> > - /* re-base the last cycle value */
> > - tk->clock->cycle_last = tk->clock->read(tk->clock);
> > + /*
> > + * 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) {
> > +
> > + cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
> > + nsec = clocksource_cyc2ns(cycle_delta, clock->mult,
> > + clock->shift);
> > + ts_delta = ns_to_timespec(nsec);
> > + } else if (timespec_compare(&ts_new, &timekeeping_suspend_time) > 0)
> > + ts_delta = timespec_sub(ts_new, timekeeping_suspend_time);
> > +
> > + if (ts_delta.tv_sec >= 1)
> > + __timekeeping_inject_sleeptime(tk, &ts_delta);
>
> If the suspend time measured by the nonstop clocksource is 0.999 sec
> then we throw it away and then let the RTC code inject inaccurate
> sleep time? Brilliant design, really.
Emm, I wrote the code with an assumption that the sleep itself and the
enter/exit processes will be longer than 1 second.
I can initialize the ts_delta to (0, 0} and change the check condition
to
if (ts_delta.tv_sec || ts_delta.tv_nsec)
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