The documentation of schedule_hrtimeout_range already states, that RT
and DL tasks do not have a timer slack. However, no information about PI
boosted tasks is given. The current implementation consistently ignores
the timer slack also for PI boosted tasks (all tasks with a rt priority
at time of programming the timer).

This patch improves the documentation by stating that the timer slack is
also ignored for PI boosted tasks. It does not include any functional
change.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index b8ee320208d4..2b1469f61d9c 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2311,7 +2311,7 @@ EXPORT_SYMBOL_GPL(schedule_hrtimeout_range_clock);
  *
  * The @delta argument gives the kernel the freedom to schedule the
  * actual wakeup to a time that is both power and performance friendly
- * for regular (non RT/DL) tasks.
+ * for regular (non RT/DL or PI boosted) tasks.
  * The kernel give the normal best effort behavior for "@expires+@delta",
  * but may decide to fire the timer earlier, but no earlier than @expires.
  *
-- 
2.39.2

On Mon, Aug 05 2024 at 14:41, Felix Moessbauer wrote:
> The documentation of schedule_hrtimeout_range already states, that RT
> and DL tasks do not have a timer slack. However, no information about PI
> boosted tasks is given. The current implementation consistently ignores
> the timer slack also for PI boosted tasks (all tasks with a rt priority
> at time of programming the timer).

Which is wrong. This condition should not use rt_task() it should use
task_is_realtime() instead.

> This patch improves the documentation by stating that the timer slack
> is

git grep "This patch" Documentation/process/

Thanks,

        tglx

On 2024-08-05 15:02:00 [+0200], Thomas Gleixner wrote:
> On Mon, Aug 05 2024 at 14:41, Felix Moessbauer wrote:
> > The documentation of schedule_hrtimeout_range already states, that RT
> > and DL tasks do not have a timer slack. However, no information about PI
> > boosted tasks is given. The current implementation consistently ignores
> > the timer slack also for PI boosted tasks (all tasks with a rt priority
> > at time of programming the timer).
> 
> Which is wrong. This condition should not use rt_task() it should use
> task_is_realtime() instead.

There is also the series 20240610192018.1567075-1-qyousef@layalina.io

> Thanks,
> 
>         tglx

Sebastian