Re: [PATCH v2] sched/rt: Clean up usage of rt_task()

On 05/29/24 12:55, Sebastian Andrzej Siewior wrote:

On 2024-05-29 11:34:09 [+0100], Qais Yousef wrote:

quoted

quoted

behaviour. But then it is insistent which matters only in the RT case.
Puh. Any sched folks regarding policy?

I am not sure I understood you here. Could you rephrase please?

Right now a SCHED_OTHER task boosted to a realtime priority gets
slack=0. In the !RT scenario everything is fine.
For RT the slack=0 also happens but the init of the timer looks at the
policy instead at the possible boosted priority and uses a different
clock attribute. This can lead to a delayed wake up (so avoiding the
slack does not solve the problem).

This is not consistent because IMHO the clock setup & slack should be
handled equally. So I am asking the sched folks for a policy and I am
leaning towards looking at task-policy in this case instead of prio
because you shouldn't do anything that can delay.

Can't we do that based on is_soft/is_hard flag in hrtimer struct when we apply
the slack in hrtimer_set_expires_range_ns() instead?

(not compile tested even)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index aa1e65ccb615..e001f20bbea9 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h

@@ -102,12 +102,16 @@ static inline void hrtimer_set_expires(struct hrtimer *timer, ktime_t time)
 
 static inline void hrtimer_set_expires_range(struct hrtimer *timer, ktime_t time, ktime_t delta)
 {
+       if (timer->is_soft || timer->is_hard)
+               delta = 0;
        timer->_softexpires = time;
        timer->node.expires = ktime_add_safe(time, delta);
 }
 
 static inline void hrtimer_set_expires_range_ns(struct hrtimer *timer, ktime_t time, u64 delta)
 {
+       if (timer->is_soft || timer->is_hard)
+               delta = 0;
        timer->_softexpires = time;
        timer->node.expires = ktime_add_safe(time, ns_to_ktime(delta));
 }