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? > > Thanks, > Rafael >
