On Fri, Sep 14, 2018 at 11:53 AM Mika Penttilä <mika.penttila@xxxxxxxxxxxx> wrote: > > On 09/14/2018 11:46 AM, Rafael J. Wysocki wrote: > > 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.wysocki@xxxxxxxxx> > >>> > >>> 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.wysocki@xxxxxxxxx> > >>> --- > >>> > >>> 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. > > I said incorrectly monotonic clock, but timekeeping_inject_sleeptime64() forwards the wall time, by the amount of delta. > Why wouldn't some other cpu update xtime when one cpu is in the loop? And if all cpus enter s2idle, tick_unfreeze() > injects sleeptime. My point is that this extra injection makes wall time wrong, no? OK, you're right. I got that the other way around. So, the patch is withdrawn.
