On Friday, September 14, 2018 10:28:44 AM CEST Mika Penttilä wrote: > Hi! > > > On 09/14/2018 09:59 AM, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > > > There is a difference in behavior between suspend-to-idle and > > suspend-to-RAM in the timekeeping handling that leads to functional > > issues. Namely, every iteration of the loop in s2idle_loop() > > increases the monotinic clock somewhat, even if timekeeping_suspend() > > and timekeeping_resume() are invoked from s2idle_enter(), and if > > many of them are carried out in a row, the monotonic clock can grow > > significantly while the system is regarded as suspended, which > > doesn't happen during suspend-to-RAM and so it is unexpected and > > leads to confusion and misbehavior in user space (similar to what > > ensued when we tried to combine the boottime and monotonic clocks). > > > > To avoid that, count all iterations of the loop in s2idle_loop() > > as "sleep time" and adjust the clock for that on exit from > > suspend-to-idle. > > > > [That also covers systems on which timekeeping is not suspended > > by by s2idle_enter().] > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > --- > > > > This is a replacement for https://patchwork.kernel.org/patch/10599209/ > > > > I decided to count the entire loop in s2idle_loop() as "sleep time" as the > > patch is then simpler and it also covers systems where timekeeping is not > > suspended in the final step of suspend-to-idle. > > > > I dropped the "Fixes:" tag, because the monotonic clock delta problem > > has been present on the latter since the very introduction of "freeze" > > (as suspend-to-idle was referred to previously) and so this doesn't fix > > any particular later commits. > > > > --- > > kernel/power/suspend.c | 18 ++++++++++++++++++ > > 1 file changed, 18 insertions(+) > > > > Index: linux-pm/kernel/power/suspend.c > > =================================================================== > > --- linux-pm.orig/kernel/power/suspend.c > > +++ linux-pm/kernel/power/suspend.c > > @@ -109,8 +109,12 @@ static void s2idle_enter(void) > > > > static void s2idle_loop(void) > > { > > + ktime_t start, delta; > > + > > pm_pr_dbg("suspend-to-idle\n"); > > > > + start = ktime_get(); > > + > > for (;;) { > > int error; > > > > @@ -150,6 +154,20 @@ static void s2idle_loop(void) > > pm_wakeup_clear(false); > > } > > > > + /* > > + * If the monotonic clock difference between the start of the loop and > > + * this point is too large, user space may get confused about whether or > > + * not the system has been suspended and tasks may get killed by > > + * watchdogs etc., so count the loop as "sleep time" to compensate for > > + * that. > > + */ > > + delta = ktime_sub(ktime_get(), start); > > + if (ktime_to_ns(delta) > 0) { > > + struct timespec64 timespec64_delta = ktime_to_timespec64(delta); > > + > > + timekeeping_inject_sleeptime64(×pec64_delta); > > + } > > But doesn't injecting sleep time here make monotonic clock too large by the > amount of sleeptime? > tick_freeze() / tick_unfreeze() already injects the sleeptime (otherwise > delta would be 0).
No, it doesn't. The delta here is the extra time taken by the loop which hasn't been counted as sleep time yet. Thanks, Rafael