linux-toradex.git/kernel/sched/rt.c, branch v6.19

sched/proxy: Yield the donor task

2025-11-11T11:33:36+00:00

When executing a task in proxy context, handle yields as if they were
requested by the donor task. This matches the traditional PI semantics
of yield() as well.

This avoids scenario like proxy task yielding, pick next task selecting the
same previous blocked donor, running the proxy task again, etc.

Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-lkp/202510211205.1e0f5223-lkp@intel.com
Suggested-by: Peter Zijlstra 
Signed-off-by: Fernand Sieber 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://patch.msgid.link/20251106104022.195157-1-sieberf@amazon.com

sched: Add support to pick functions to take rf

2025-10-16T09:13:55+00:00

Some pick functions like the internal pick_next_task_fair() already take
rf but some others dont. We need this for scx's server pick function.
Prepare for this by having pick functions accept it.

[peterz: - added RETRY_TASK handling
         - removed pick_next_task_fair indirection]
Signed-off-by: Joel Fernandes 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Tejun Heo

sched: Detect per-class runqueue changes

2025-10-16T09:13:55+00:00

Have enqueue/dequeue set a per-class bit in rq->queue_mask. This then
enables easy tracking of which runqueues are modified over a
lock-break.

Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Tejun Heo

sched: Move sched_class::prio_changed() into the change pattern

2025-10-16T09:13:52+00:00

Move sched_class::prio_changed() into the change pattern.

And while there, extend it with sched_class::get_prio() in order to
fix the deadline sitation.

Suggested-by: Tejun Heo 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Juri Lelli 
Acked-by: Tejun Heo 
Acked-by: Vincent Guittot

sched: Fold sched_class::switch{ing,ed}_{to,from}() into the change pattern

2025-10-16T09:13:51+00:00

Add {DE,EN}QUEUE_CLASS and fold the sched_class::switch* methods into
the change pattern. This completes and makes the pattern more
symmetric.

This changes the order of callbacks slightly:

  OLD                              NEW
				|
				|  switching_from()
  dequeue_task();		|  dequeue_task()
  put_prev_task();		|  put_prev_task()
				|  switched_from()
				|
  ... change task ...		|  ... change task ...
				|
  switching_to();		|  switching_to()
  enqueue_task();		|  enqueue_task()
  set_next_task();		|  set_next_task()
  prev_class->switched_from()	|
  switched_to()			|  switched_to()
				|

Notably, it moves the switched_from() callback right after the
dequeue/put. Existing implementations don't appear to be affected by
this change in location -- specifically the task isn't enqueued on the
class in question in either location.

Make (CLASS)^(SAVE|MOVE), because there is nothing to save-restore
when changing scheduling classes.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Juri Lelli 
Acked-by: Tejun Heo 
Acked-by: Vincent Guittot

sched: Fix proxy/current (push,pull)ability

2025-07-14T15:16:33+00:00

Proxy execution forms atomic pairs of tasks: The waiting donor
task (scheduling context) and a proxy (execution context). The
donor task, along with the rest of the blocked chain, follows
the proxy wrt CPU placement.

They can be the same task, in which case push/pull doesn't need any
modification. When they are different, however,
FIFO1 & FIFO42:

	      ,->  RT42
	      |     | blocked-on
	      |     v
blocked_donor |   mutex
	      |     | owner
	      |     v
	      `--  RT1

   RT1
   RT42

  CPU0            CPU1
   ^                ^
   |                |
  overloaded    !overloaded
  rq prio = 42  rq prio = 0

RT1 is eligible to be pushed to CPU1, but should that happen it will
"carry" RT42 along. Clearly here neither RT1 nor RT42 must be seen as
push/pullable.

Unfortunately, only the donor task is usually dequeued from the rq,
and the proxy'ed execution context (rq->curr) remains on the rq.
This can cause RT1 to be selected for migration from logic like the
rt pushable_list.

Thus, adda a dequeue/enqueue cycle on the proxy task before __schedule
returns, which allows the sched class logic to avoid adding the now
current task to the pushable_list.

Furthermore, tasks becoming blocked on a mutex don't need an explicit
dequeue/enqueue cycle to be made (push/pull)able: they have to be running
to block on a mutex, thus they will eventually hit put_prev_task().

Signed-off-by: Valentin Schneider 
Signed-off-by: Connor O'Brien 
Signed-off-by: John Stultz 
Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: K Prateek Nayak 
Link: https://lkml.kernel.org/r/20250712033407.2383110-8-jstultz@google.com

sched/deadline: Fix accounting after global limits change

2025-07-14T08:59:33+00:00

A global limits change (sched_rt_handler() logic) currently leaves stale
and/or incorrect values in variables related to accounting (e.g.
extra_bw).

Properly clean up per runqueue variables before implementing the change
and rebuild scheduling domains (so that accounting is also properly
restored) after such a change is complete.

Reported-by: Marcel Ziswiler 
Signed-off-by: Juri Lelli 
Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: Marcel Ziswiler  # nuc & rock5b
Link: https://lore.kernel.org/r/20250627115118.438797-4-juri.lelli@redhat.com

sched/smp: Use the SMP version of the RT scheduling class

2025-06-13T06:47:20+00:00

Simplify the scheduler by making CONFIG_SMP=y primitives and data
structures unconditional in the RT policies scheduler.

Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra 
Cc: Dietmar Eggemann 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Cc: Mel Gorman 
Cc: Sebastian Andrzej Siewior 
Cc: Shrikanth Hegde 
Cc: Steven Rostedt 
Cc: Valentin Schneider 
Cc: Vincent Guittot 
Link: https://lore.kernel.org/r/20250528080924.2273858-29-mingo@kernel.org

sched/smp: Make SMP unconditional

2025-06-13T06:47:18+00:00

Simplify the scheduler by making CONFIG_SMP=y primitives and data
structures unconditional.

Introduce transitory wrappers for functionality not yet converted to SMP.

Note that this patch is pretty large, because there's no clear separation
between various aspects of the SMP scheduler, it's basically a huge block
of #ifdef CONFIG_SMP. A fair amount of it has to be switched on for it to
boot and work on UP systems.

Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra 
Cc: Dietmar Eggemann 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Cc: Mel Gorman 
Cc: Sebastian Andrzej Siewior 
Cc: Shrikanth Hegde 
Cc: Steven Rostedt 
Cc: Valentin Schneider 
Cc: Vincent Guittot 
Link: https://lore.kernel.org/r/20250528080924.2273858-21-mingo@kernel.org

sched: Clean up and standardize #if/#else/#endif markers in sched/rt.c

2025-06-13T06:47:17+00:00

 - Use the standard #ifdef marker format for larger blocks,
   where appropriate:

        #if CONFIG_FOO
        ...
        #else /* !CONFIG_FOO: */
        ...
        #endif /* !CONFIG_FOO */

 - Fix whitespace noise and other inconsistencies.

Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra 
Cc: Dietmar Eggemann 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Cc: Mel Gorman 
Cc: Sebastian Andrzej Siewior 
Cc: Shrikanth Hegde 
Cc: Steven Rostedt 
Cc: Valentin Schneider 
Cc: Vincent Guittot 
Link: https://lore.kernel.org/r/20250528080924.2273858-15-mingo@kernel.org