This is a note to let you know that I've just added the patch titled
hrtimer: Ignore slack time for RT tasks in schedule_hrtimeout_range()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
hrtimer-ignore-slack-time-for-rt-tasks-in-schedule_hrtimeout_range.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 0c52310f260014d95c1310364379772cb74cf82d Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Date: Mon, 23 Jan 2023 09:32:06 -0800
Subject: hrtimer: Ignore slack time for RT tasks in schedule_hrtimeout_range()
From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
commit 0c52310f260014d95c1310364379772cb74cf82d upstream.
While in theory the timer can be triggered before expires + delta, for the
cases of RT tasks they really have no business giving any lenience for
extra slack time, so override any passed value by the user and always use
zero for schedule_hrtimeout_range() calls. Furthermore, this is similar to
what the nanosleep(2) family already does with current->timer_slack_ns.
Signed-off-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230123173206.6764-3-dave@xxxxxxxxxxxx
Signed-off-by: Felix Moessbauer <felix.moessbauer@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/time/hrtimer.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2164,7 +2164,7 @@ void __init hrtimers_init(void)
/**
* schedule_hrtimeout_range_clock - sleep until timeout
* @expires: timeout value (ktime_t)
- * @delta: slack in expires timeout (ktime_t)
+ * @delta: slack in expires timeout (ktime_t) for SCHED_OTHER tasks
* @mode: timer mode
* @clock_id: timer clock to be used
*/
@@ -2191,6 +2191,13 @@ schedule_hrtimeout_range_clock(ktime_t *
return -EINTR;
}
+ /*
+ * Override any slack passed by the user if under
+ * rt contraints.
+ */
+ if (rt_task(current))
+ delta = 0;
+
hrtimer_init_sleeper_on_stack(&t, clock_id, mode);
hrtimer_set_expires_range_ns(&t.timer, *expires, delta);
hrtimer_sleeper_start_expires(&t, mode);
@@ -2210,7 +2217,7 @@ EXPORT_SYMBOL_GPL(schedule_hrtimeout_ran
/**
* schedule_hrtimeout_range - sleep until timeout
* @expires: timeout value (ktime_t)
- * @delta: slack in expires timeout (ktime_t)
+ * @delta: slack in expires timeout (ktime_t) for SCHED_OTHER tasks
* @mode: timer mode
*
* Make the current task sleep until the given expiry time has
@@ -2218,7 +2225,8 @@ EXPORT_SYMBOL_GPL(schedule_hrtimeout_ran
* the current task state has been set (see set_current_state()).
*
* The @delta argument gives the kernel the freedom to schedule the
- * actual wakeup to a time that is both power and performance friendly.
+ * actual wakeup to a time that is both power and performance friendly
+ * for regular (non RT/DL) 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.
*
Patches currently in stable-queue which might be from dave@xxxxxxxxxxxx are
queue-5.10/hrtimer-ignore-slack-time-for-rt-tasks-in-schedule_hrtimeout_range.patch
