[v10,2/6] arm64: idle: Tag the arm64 idle functions as __cpuidle

Commit Message

Doug Anderson Aug. 22, 2023, 9:26 p.m. UTC

As per the (somewhat recent) comment before the definition of
`__cpuidle`, the tag is like `noinstr` but also marks a function so it
can be identified by cpu_in_idle(). Let'a add this.

After doing this then when we dump stack traces of all processors
using nmi_cpu_backtrace() then instead of getting useless backtraces
we get things like:

  NMI backtrace for cpu N skipped: idling at cpu_do_idle+0x94/0x98

NOTE: this patch won't make cpu_in_idle() work perfectly for arm64,
but it doesn't hurt and does catch some cases. Specifically an example
that wasn't caught in my testing looked like this:

 gic_cpu_sys_reg_init+0x1f8/0x314
 gic_cpu_pm_notifier+0x40/0x78
 raw_notifier_call_chain+0x5c/0x134
 cpu_pm_notify+0x38/0x64
 cpu_pm_exit+0x20/0x2c
 psci_enter_idle_state+0x48/0x70
 cpuidle_enter_state+0xb8/0x260
 cpuidle_enter+0x44/0x5c
 do_idle+0x188/0x30c

Acked-by: Mark Rutland <[e-mail]>
Signed-off-by: Douglas Anderson <[e-mail]>
---

(no changes since v9)

Changes in v9:
- Added to commit message that this doesn't catch all cases.

Changes in v8:
- "Tag the arm64 idle functions as __cpuidle" new for v8

 arch/arm64/kernel/idle.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Stephen Boyd Aug. 22, 2023, 11:14 p.m. UTC | #1

Quoting Douglas Anderson (2023-08-22 14:26:57)
> As per the (somewhat recent) comment before the definition of
> `__cpuidle`, the tag is like `noinstr` but also marks a function so it
> can be identified by cpu_in_idle(). Let'a add this.

s/Let'a/Let's/

Maybe also define "this" to be "Let's add these markings to arm64
cpuidle functions".

>
> After doing this then when we dump stack traces of all processors
> using nmi_cpu_backtrace() then instead of getting useless backtraces
> we get things like:

Sorry, this sentence is really hard for me to read. Perhaps:

With this change we get useful backtraces like:

   NMI backtrace for cpu N skipped: idling at cpu_do_idle+0x94/0x98

instead of useless backtraces when dumping all processors using
nmi_cpu_backtrace().

>
>   NMI backtrace for cpu N skipped: idling at cpu_do_idle+0x94/0x98
>
> NOTE: this patch won't make cpu_in_idle() work perfectly for arm64,
> but it doesn't hurt and does catch some cases. Specifically an example
> that wasn't caught in my testing looked like this:

I wonder if it improves locality of cpu idle code as well by moving the
functions to the idle text section so any branch targets are closer.

>
>  gic_cpu_sys_reg_init+0x1f8/0x314
>  gic_cpu_pm_notifier+0x40/0x78
>  raw_notifier_call_chain+0x5c/0x134
>  cpu_pm_notify+0x38/0x64
>  cpu_pm_exit+0x20/0x2c
>  psci_enter_idle_state+0x48/0x70
>  cpuidle_enter_state+0xb8/0x260
>  cpuidle_enter+0x44/0x5c
>  do_idle+0x188/0x30c
>
> Acked-by: Mark Rutland <[e-mail]>
> Signed-off-by: Douglas Anderson <[e-mail]>

Reviewed-by: Stephen Boyd <[e-mail]>

Patch

diff --git a/arch/arm64/kernel/idle.c b/arch/arm64/kernel/idle.c
index c1125753fe9b..05cfb347ec26 100644
--- a/arch/arm64/kernel/idle.c
+++ b/arch/arm64/kernel/idle.c
@@ -20,7 +20,7 @@ 
  *	ensure that interrupts are not masked at the PMR (because the core will
  *	not wake up if we block the wake up signal in the interrupt controller).
  */
-void noinstr cpu_do_idle(void)
+void __cpuidle cpu_do_idle(void)
 {
 	struct arm_cpuidle_irq_context context;
 
@@ -35,7 +35,7 @@  void noinstr cpu_do_idle(void)
 /*
  * This is our default idle handler.
  */
-void noinstr arch_cpu_idle(void)
+void __cpuidle arch_cpu_idle(void)
 {
 	/*
 	 * This should do all the clock switching and wait for interrupt