Re: [RFC][PATCH 4/4] acpi: Take over RCU-idle for C3-BM idle

[Guenter Roeck]

On Tue, Sep 15, 2020 at 12:32:01PM +0200, Peter Zijlstra wrote:
> The C3 BusMaster idle code takes lock in a number of places, some deep
> inside the ACPI code. Instead of wrapping it all in RCU_NONIDLE, have
> the driver take over RCU-idle duty and avoid flipping RCU state back
> and forth a lot.
> 
> ( by marking 'C3 && bm_check' as RCU_IDLE, we _must_ call enter_bm() for
>   that combination, otherwise we'll loose RCU-idle, this requires
>   shuffling some code around )
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

ia64:defconfig:

ERROR: modpost: "rcu_idle_enter" [drivers/acpi/processor.ko] undefined!
ERROR: modpost: "rcu_idle_exit" [drivers/acpi/processor.ko] undefined!

I realize that this has already been reported more than a week ago, with
no visible reaction. Another problem introduced in the same file, resulting
in

drivers/acpi/processor_idle.c: In function 'lapic_timer_needs_broadcast':
drivers/acpi/processor_idle.c:179:1: warning:
	no return statement in function returning non-void

may cause ia64 boot problems since a non-zero return value will trigger
a function call. AFAICS that is not supposed to happen on ia64.

This makes me wonder - if no one cares about buiding (much less running)
ia64 images with the upstream kernel, is it possibly time to remove it ?

Guenter