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

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Date:   Fri, 25 Sep 2020 08:29:05 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Peter Zijlstra <peterz@...radead.org>, rjw@...ysocki.net,
        bp@...en8.de, x86@...nel.org, tony.luck@...el.com, lenb@...nel.org,
        daniel.lezcano@...aro.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        ulf.hansson@...aro.org, tglx@...utronix.de,
        naresh.kamboju@...aro.org
Subject: Re: [RFC][PATCH 4/4] acpi: Take over RCU-idle for C3-BM idle

On Fri, Sep 25, 2020 at 08:20:00AM -0700, Guenter Roeck 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@...radead.org>
> 
> 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 ?

Rafael is taking a fix up his cpuidle tree:

https://lkml.kernel.org/lkml/CAJZ5v0jVerU92WxL4qCoU6NC0KCyszmRNhpL3tu5LYtMqALd9A@mail.gmail.com/

							Thanx, Paul