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

[Stephen Boyd]

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 <mark.rutland@xxxxxxx>
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>