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

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Date:	Thu, 25 Apr 2013 23:01:02 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Stephen Boyd <sboyd@...eaurora.org>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	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 Thu, 25 Apr 2013, Stephen Boyd wrote:
> 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?

If the patch is agreed on, I guess I should take it via my idle
consolidation branch, right ?

 
> ----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
> 
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> hosted by The Linux Foundation
> 
> 
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