linux-kernel - Re: [patch 08/34] arm: Use generic idle loop

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Message-ID: <51798C1D.9090405@codeaurora.org>
Date:	Thu, 25 Apr 2013 13:03:41 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Kevin Hilman <khilman@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Magnus Damm <magnus.damm@...il.com>
Subject: Re: [patch 08/34] arm: Use generic idle loop

On 04/09/13 02:38, Russell King - ARM Linux wrote:
> On Tue, Apr 09, 2013 at 11:20:31AM +0200, Thomas Gleixner wrote:
>> On Mon, 8 Apr 2013, Russell King - ARM Linux wrote:
>>> On Mon, Mar 25, 2013 at 03:02:39PM +0100, Thomas Gleixner wrote:
>>> So, how can I review these changes when all there is is a git URL, and
>>> I *do* not want to pull them into my tree without first looking at the
>>> patches, possibly reviewing them and *replying* with the patch inline?
>> the patches were CC'ed to LKML and linux-arch and I expected that you
>> are at least having the latter. Find the relevant patch inlined below.
> I've not been on linux-arch for a few years now, after it evolved into
> yet another lkml-like list with high traffic rates, where mainly specific
> x86 issues seemed to be discussed, rather than it being a way to contact
> all arch maintainers.
>
>> It is a counter. I looked carefully at all the various slightly
>> differently fcked up implementations and picked the counter based one
>> as it fits all requirements.
> Great, thanks.  The attached patch looks fine to me.

I'm pretty sure that we need to apply this patch now that
rcu_idle_enter()/exit() is called lower down in the idle loop. Kevin,
did you test hotplug?

----8<-----

From: Stephen Boyd <sboyd@...eaurora.org>
Subject: [PATCH] ARM: smp: Drop RCU_NONIDLE usage in cpu_die()

Before f7b861b (arm: Use generic idle loop, 2013-03-21) ARM would
kill the CPU within the rcu idle section. Now that the
rcu_idle_enter()/exit() pair have been pushed lower down in the
idle loop this is no longer true and so using RCU_NONIDLE here is
no longer necessary and also harmful because RCU is not actually
idle at this point.

Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
---
 arch/arm/kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 4619177..78f1eb5 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -233,7 +233,7 @@ void __ref cpu_die(void)
        mb();
 
        /* Tell __cpu_die() that this CPU is now safe to dispose of */
-       RCU_NONIDLE(complete(&cpu_died));
+       complete(&cpu_died);
 
        /*
         * actual CPU shutdown procedure is at least platform (if not

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