linux-stable.git/kernel/sched/idle.c, branch linux-6.6.y

sched: idle: Consolidate the handling of two special cases

2026-03-25T10:06:07+00:00

[ Upstream commit f4c31b07b136839e0fb3026f8a5b6543e3b14d2f ]

There are two special cases in the idle loop that are handled
inconsistently even though they are analogous.

The first one is when a cpuidle driver is absent and the default CPU
idle time power management implemented by the architecture code is used.
In that case, the scheduler tick is stopped every time before invoking
default_idle_call().

The second one is when a cpuidle driver is present, but there is only
one idle state in its table.  In that case, the scheduler tick is never
stopped at all.

Since each of these approaches has its drawbacks, reconcile them with
the help of one simple heuristic.  Namely, stop the tick if the CPU has
been woken up by it in the previous iteration of the idle loop, or let
it tick otherwise.

Signed-off-by: Rafael J. Wysocki 
Reviewed-by: Christian Loehle 
Reviewed-by: Frederic Weisbecker 
Reviewed-by: Qais Yousef 
Reviewed-by: Aboorva Devarajan 
Fixes: ed98c3491998 ("sched: idle: Do not stop the tick before cpuidle_idle_call()")
[ rjw: Added Fixes tag, changelog edits ]
Link: https://patch.msgid.link/4741364.LvFx2qVVIh@rafael.j.wysocki
Signed-off-by: Rafael J. Wysocki 
Signed-off-by: Sasha Levin

sched/fair: Fix pelt clock sync when entering idle

2026-03-25T10:06:01+00:00

[ Upstream commit 98c88dc8a1ace642d9021b103b28cba7b51e3abc ]

Samuel and Alex reported regressions of the util_avg of RT rq with
commit 17e3e88ed0b6 ("sched/fair: Fix pelt lost idle time detection").
It happens that fair is updating and syncing the pelt clock with task one
when pick_next_task_fair() fails to pick a task but before the prev
scheduling class got a chance to update its pelt signals.

Move update_idle_rq_clock_pelt() in set_next_task_idle() which is called
after prev class has been called.

Fixes: 17e3e88ed0b6 ("sched/fair: Fix pelt lost idle time detection")
Reported-by: Samuel Wu 
Closes: https://lore.kernel.org/all/CAG2KctpO6VKS6GN4QWDji0t92_gNBJ7HjjXrE+6H+RwRXt=iLg@mail.gmail.com/
Reported-by: Alex Hoh 
Closes: https://lore.kernel.org/all/8cf19bf0e0054dcfed70e9935029201694f1bb5a.camel@mediatek.com/
Signed-off-by: Vincent Guittot 
Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: Samuel Wu 
Tested-by: Alex Hoh 
Link: https://patch.msgid.link/20260121163317.505635-1-vincent.guittot@linaro.org
(cherry picked from commit 98c88dc8a1ace642d9021b103b28cba7b51e3abc)
[ wusamuel: Did not include line 'exec_start = rq_clock_task()', which
is not present in 6.6.y but found in mainline ]
Signed-off-by: Samuel Wu 
Signed-off-by: Greg Kroah-Hartman

sched: idle: Make skipping governor callbacks more consistent

2026-03-25T10:05:47+00:00

[ Upstream commit d557640e4ce589a24dca5ca7ce3b9680f471325f ]

If the cpuidle governor .select() callback is skipped because there
is only one idle state in the cpuidle driver, the .reflect() callback
should be skipped as well, at least for consistency (if not for
correctness), so do it.

Fixes: e5c9ffc6ae1b ("cpuidle: Skip governor when only one idle state is available")
Signed-off-by: Rafael J. Wysocki 
Reviewed-by: Christian Loehle 
Reviewed-by: Aboorva Devarajan 
Reviewed-by: Frederic Weisbecker 
Link: https://patch.msgid.link/12857700.O9o76ZdvQC@rafael.j.wysocki
Signed-off-by: Sasha Levin

sched/fair: Rename check_preempt_curr() to wakeup_preempt()

2024-12-14T19:00:18+00:00

[ Upstream commit e23edc86b09df655bf8963bbcb16647adc787395 ]

The name is a bit opaque - make it clear that this is about wakeup
preemption.

Also rename the ->check_preempt_curr() methods similarly.

Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra (Intel) 
Stable-dep-of: 0664e2c311b9 ("sched/deadline: Fix warning in migrate_enable for boosted tasks")
Signed-off-by: Sasha Levin

kernel/sched: Modify initial boot task idle setup

2023-09-19T08:48:04+00:00

Initial booting is setting the task flag to idle (PF_IDLE) by the call
path sched_init() -> init_idle().  Having the task idle and calling
call_rcu() in kernel/rcu/tiny.c means that TIF_NEED_RESCHED will be
set.  Subsequent calls to any cond_resched() will enable IRQs,
potentially earlier than the IRQ setup has completed.  Recent changes
have caused just this scenario and IRQs have been enabled early.

This causes a warning later in start_kernel() as interrupts are enabled
before they are fully set up.

Fix this issue by setting the PF_IDLE flag later in the boot sequence.

Although the boot task was marked as idle since (at least) d80e4fda576d,
I am not sure that it is wrong to do so.  The forced context-switch on
idle task was introduced in the tiny_rcu update, so I'm going to claim
this fixes 5f6130fa52ee.

Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task")
Signed-off-by: Liam R. Howlett 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/linux-mm/CAMuHMdWpvpWoDa=Ox-do92czYRvkok6_x6pYUH+ZouMcJbXy+Q@mail.gmail.com/

sched/idle: Mark arch_cpu_idle_dead() __noreturn

2023-03-08T16:44:28+00:00

Before commit 076cbf5d2163 ("x86/xen: don't let xen_pv_play_dead()
return"), in Xen, when a previously offlined CPU was brought back
online, it unexpectedly resumed execution where it left off in the
middle of the idle loop.

There were some hacks to make that work, but the behavior was surprising
as do_idle() doesn't expect an offlined CPU to return from the dead (in
arch_cpu_idle_dead()).

Now that Xen has been fixed, and the arch-specific implementations of
arch_cpu_idle_dead() also don't return, give it a __noreturn attribute.

This will cause the compiler to complain if an arch-specific
implementation might return.  It also improves code generation for both
caller and callee.

Also fixes the following warning:

  vmlinux.o: warning: objtool: do_idle+0x25f: unreachable instruction

Reported-by: Paul E. McKenney 
Tested-by: Paul E. McKenney 
Link: https://lore.kernel.org/r/60d527353da8c99d4cf13b6473131d46719ed16d.1676358308.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf

sched/idle: Make sure weak version of arch_cpu_idle_dead() doesn't return

2023-03-08T16:44:27+00:00

arch_cpu_idle_dead() should never return.  Make it so.

Link: https://lore.kernel.org/r/cf5ad95eef50f7704bb30e7770c59bfe23372af7.1676358308.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf

arch/idle: Change arch_cpu_idle() behavior: always exit with IRQs disabled

2023-01-13T10:48:15+00:00

Current arch_cpu_idle() is called with IRQs disabled, but will return
with IRQs enabled.

However, the very first thing the generic code does after calling
arch_cpu_idle() is raw_local_irq_disable(). This means that
architectures that can idle with IRQs disabled end up doing a
pointless 'enable-disable' dance.

Therefore, push this IRQ disabling into the idle function, meaning
that those architectures can avoid the pointless IRQ state flipping.

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Tested-by: Tony Lindgren 
Tested-by: Ulf Hansson 
Reviewed-by: Gautham R. Shenoy 
Acked-by: Mark Rutland  [arm64]
Acked-by: Rafael J. Wysocki 
Acked-by: Guo Ren 
Acked-by: Frederic Weisbecker 
Link: https://lore.kernel.org/r/20230112195540.618076436@infradead.org

cpuidle: Fix ct_idle_*() usage

2023-01-13T10:48:15+00:00

The whole disable-RCU, enable-IRQS dance is very intricate since
changing IRQ state is traced, which depends on RCU.

Add two helpers for the cpuidle case that mirror the entry code:

  ct_cpuidle_enter()
  ct_cpuidle_exit()

And fix all the cases where the enter/exit dance was buggy.

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Tested-by: Tony Lindgren 
Tested-by: Ulf Hansson 
Acked-by: Rafael J. Wysocki 
Acked-by: Frederic Weisbecker 
Link: https://lore.kernel.org/r/20230112195540.130014793@infradead.org

context_tracking: Take idle eqs entrypoints over RCU

2022-07-05T20:32:16+00:00

The RCU dynticks counter is going to be merged into the context tracking
subsystem. Start with moving the idle extended quiescent states
entrypoints to context tracking. For now those are dumb redirections to
existing RCU calls.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Frederic Weisbecker 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Neeraj Upadhyay 
Cc: Uladzislau Rezki 
Cc: Joel Fernandes 
Cc: Boqun Feng 
Cc: Nicolas Saenz Julienne 
Cc: Marcelo Tosatti 
Cc: Xiongfeng Wang 
Cc: Yu Liao 
Cc: Phil Auld 
Cc: Paul Gortmaker
Cc: Alex Belits 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Nicolas Saenz Julienne 
Tested-by: Nicolas Saenz Julienne