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

[Rafael J. Wysocki]

On Fri, Sep 25, 2020 at 5:20 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> 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.

There are fixes for the above in my tree, they will go to Linus shortly.

Thanks!