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SubjectRe: [PATCH] PM / suspend: Count suspend-to-idle loop as sleep time
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Hi!


On 09/14/2018 09:59 AM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@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.wysocki@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(&timespec64_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).

> +
> pm_pr_dbg("resume from suspend-to-idle\n");
> }
>
>

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