[1/2] PM-runtime: move runtime accounting on ktime_get_mono_fast_ns()
diff mbox series

Message ID 1549297553-17647-2-git-send-email-vincent.guittot@linaro.org
State Under Review
Delegated to: Geert Uytterhoeven
Headers show
Series
  • PM-runtime: fix and clean up of time accounting
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Commit Message

Vincent Guittot Feb. 4, 2019, 4:25 p.m. UTC
Similarly to what happened whith autosuspend, a deadlock has been raised
with runtime accounting in the sequence:

change_clocksource
    ...
    write_seqcount_begin
    ...
    timekeeping_update
        ...
        sh_cmt_clocksource_enable
            ...
            rpm_resume
                update_pm_runtime_accounting
                    ktime_get
                        do
                            read_seqcount_begin
                        while read_seqcount_retry
    ....
    write_seqcount_end

Move runtime accounting on ktime_get_mono_fast_ns()
With ktime_get_mono_fast_ns, the timestamp is not guaranteed to be
monotonic across an update of timekeeping and as a result time can goes
backward. Add a test to skip accounting for such situation which should
stay exceptional.

Fixes: a08c2a5a3194 ("PM-runtime: Replace jiffies-based accounting with ktime-based accounting")
Reported-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 drivers/base/power/runtime.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

Comments

Ulf Hansson Feb. 5, 2019, 8:09 a.m. UTC | #1
On Mon, 4 Feb 2019 at 17:25, Vincent Guittot <vincent.guittot@linaro.org> wrote:
>
> Similarly to what happened whith autosuspend, a deadlock has been raised
> with runtime accounting in the sequence:
>
> change_clocksource
>     ...
>     write_seqcount_begin
>     ...
>     timekeeping_update
>         ...
>         sh_cmt_clocksource_enable
>             ...
>             rpm_resume
>                 update_pm_runtime_accounting
>                     ktime_get
>                         do
>                             read_seqcount_begin
>                         while read_seqcount_retry
>     ....
>     write_seqcount_end
>
> Move runtime accounting on ktime_get_mono_fast_ns()
> With ktime_get_mono_fast_ns, the timestamp is not guaranteed to be
> monotonic across an update of timekeeping and as a result time can goes
> backward. Add a test to skip accounting for such situation which should
> stay exceptional.
>
> Fixes: a08c2a5a3194 ("PM-runtime: Replace jiffies-based accounting with ktime-based accounting")
> Reported-by: Biju Das <biju.das@bp.renesas.com>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe


> ---
>  drivers/base/power/runtime.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 1caa394..50740da 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -66,13 +66,22 @@ static int rpm_suspend(struct device *dev, int rpmflags);
>   */
>  void update_pm_runtime_accounting(struct device *dev)
>  {
> -       u64 now = ktime_to_ns(ktime_get());
> +       u64 now = ktime_get_mono_fast_ns();
> +       u64 last = dev->power.accounting_timestamp;
>         u64 delta;
>
> -       delta = now - dev->power.accounting_timestamp;
> -
>         dev->power.accounting_timestamp = now;
>
> +       /*
> +        * Because ktime_get_mono_fast_ns() is not monotonic during
> +        * timekeeping update, we must ensure that now is after the last saved
> +        * timesptamp
> +        */
> +       if (now < last)
> +               return;
> +
> +       delta = now - last;
> +
>         if (dev->power.disable_depth > 0)
>                 return;
>
> @@ -1312,7 +1321,7 @@ void pm_runtime_enable(struct device *dev)
>
>                 /* About to enable runtime pm, set accounting_timestamp to now */
>                 if (!dev->power.disable_depth)
> -                       dev->power.accounting_timestamp = ktime_to_ns(ktime_get());
> +                       dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
>         } else {
>                 dev_warn(dev, "Unbalanced %s!\n", __func__);
>         }
> --
> 2.7.4
>
Vincent Guittot Feb. 5, 2019, 8:39 a.m. UTC | #2
On Tue, 5 Feb 2019 at 09:10, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> On Mon, 4 Feb 2019 at 17:25, Vincent Guittot <vincent.guittot@linaro.org> wrote:
> >
> > Similarly to what happened whith autosuspend, a deadlock has been raised
> > with runtime accounting in the sequence:
> >
> > change_clocksource
> >     ...
> >     write_seqcount_begin
> >     ...
> >     timekeeping_update
> >         ...
> >         sh_cmt_clocksource_enable
> >             ...
> >             rpm_resume
> >                 update_pm_runtime_accounting
> >                     ktime_get
> >                         do
> >                             read_seqcount_begin
> >                         while read_seqcount_retry
> >     ....
> >     write_seqcount_end
> >
> > Move runtime accounting on ktime_get_mono_fast_ns()
> > With ktime_get_mono_fast_ns, the timestamp is not guaranteed to be
> > monotonic across an update of timekeeping and as a result time can goes
> > backward. Add a test to skip accounting for such situation which should
> > stay exceptional.
> >
> > Fixes: a08c2a5a3194 ("PM-runtime: Replace jiffies-based accounting with ktime-based accounting")
> > Reported-by: Biju Das <biju.das@bp.renesas.com>
> > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
>
> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Thanks

>
> Kind regards
> Uffe
>
>
> > ---
> >  drivers/base/power/runtime.c | 17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> > index 1caa394..50740da 100644
> > --- a/drivers/base/power/runtime.c
> > +++ b/drivers/base/power/runtime.c
> > @@ -66,13 +66,22 @@ static int rpm_suspend(struct device *dev, int rpmflags);
> >   */
> >  void update_pm_runtime_accounting(struct device *dev)
> >  {
> > -       u64 now = ktime_to_ns(ktime_get());
> > +       u64 now = ktime_get_mono_fast_ns();
> > +       u64 last = dev->power.accounting_timestamp;
> >         u64 delta;
> >
> > -       delta = now - dev->power.accounting_timestamp;
> > -
> >         dev->power.accounting_timestamp = now;
> >
> > +       /*
> > +        * Because ktime_get_mono_fast_ns() is not monotonic during
> > +        * timekeeping update, we must ensure that now is after the last saved
> > +        * timesptamp
> > +        */
> > +       if (now < last)
> > +               return;
> > +
> > +       delta = now - last;
> > +
> >         if (dev->power.disable_depth > 0)
> >                 return;
> >
> > @@ -1312,7 +1321,7 @@ void pm_runtime_enable(struct device *dev)
> >
> >                 /* About to enable runtime pm, set accounting_timestamp to now */
> >                 if (!dev->power.disable_depth)
> > -                       dev->power.accounting_timestamp = ktime_to_ns(ktime_get());
> > +                       dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
> >         } else {
> >                 dev_warn(dev, "Unbalanced %s!\n", __func__);
> >         }
> > --
> > 2.7.4
> >

Patch
diff mbox series

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 1caa394..50740da 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -66,13 +66,22 @@  static int rpm_suspend(struct device *dev, int rpmflags);
  */
 void update_pm_runtime_accounting(struct device *dev)
 {
-	u64 now = ktime_to_ns(ktime_get());
+	u64 now = ktime_get_mono_fast_ns();
+	u64 last = dev->power.accounting_timestamp;
 	u64 delta;
 
-	delta = now - dev->power.accounting_timestamp;
-
 	dev->power.accounting_timestamp = now;
 
+	/*
+	 * Because ktime_get_mono_fast_ns() is not monotonic during
+	 * timekeeping update, we must ensure that now is after the last saved
+	 * timesptamp
+	 */
+	if (now < last)
+		return;
+
+	delta = now - last;
+
 	if (dev->power.disable_depth > 0)
 		return;
 
@@ -1312,7 +1321,7 @@  void pm_runtime_enable(struct device *dev)
 
 		/* About to enable runtime pm, set accounting_timestamp to now */
 		if (!dev->power.disable_depth)
-			dev->power.accounting_timestamp = ktime_to_ns(ktime_get());
+			dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
 	} else {
 		dev_warn(dev, "Unbalanced %s!\n", __func__);
 	}