On Fri, Sep 14, 2018 at 08:59:03AM +0200, 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>
Do we want a 'warning' of sorts when the delta becomes significant (for
whatever that is) ? That might be an indication that there are frequent
wakeups which we might not be expecting. Of keep the number of spurious
wakeups in a stat counter somewhere -- something to look at if the
battery drains faster than expected.
Otherwise:
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
One minor nit below:
> ---
> 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);
> + }
> +
> pm_pr_dbg("resume from suspend-to-idle\n");
> }
Like I mentioned yesterday; I myself prefer the form:
u64 stamp = ktimer_get_ns();
for (;;) {
/* ... */
}
stamp = ktime_get_ns() - stamp;
if (stamp)
timekeeping_inject_sleeptime64(ns_to_timespec64(ns));
Esp. since ktime_t _is_ s64 these days, there is no point in keep using
all the weird ktime helpers that make the code harder to read.
