linux-kernel - Re: [PATCH 08/10] parisc: Add missing RCU idle APIs on idle loop

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Date:	Fri, 24 Aug 2012 09:26:47 -0400
From:	John David Anglin <dave.anglin@...l.net>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Helge Deller <deller@....de>,
	Parisc <linux-parisc@...r.kernel.org>,
	"3.2.x.." <stable@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 08/10] parisc: Add missing RCU idle APIs on idle loop

On 8/22/2012 12:23 PM, Frederic Weisbecker wrote:
> In the old times, the whole idle task was considered
> as an RCU quiescent state. But as RCU became more and
> more successful overtime, some RCU read side critical
> section have been added even in the code of some
> architectures idle tasks, for tracing for example.
>
> So nowadays, rcu_idle_enter() and rcu_idle_exit() must
> be called by the architecture to tell RCU about the part
> in the idle loop that doesn't make use of rcu read side
> critical sections, typically the part that puts the CPU
> in low power mode.
>
> This is necessary for RCU to find the quiescent states in
> idle in order to complete grace periods.
>
> Add this missing pair of calls in the parisc's idle loop.
>
> Reported-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: James E.J. Bottomley <jejb@...isc-linux.org>
> Cc: Helge Deller <deller@....de>
> Cc: Parisc <linux-parisc@...r.kernel.org>
> Cc: 3.2.x.. <stable@...nel.org>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>   arch/parisc/kernel/process.c |    3 +++
>   1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
> index d4b94b3..c54a4db 100644
> --- a/arch/parisc/kernel/process.c
> +++ b/arch/parisc/kernel/process.c
> @@ -48,6 +48,7 @@
>   #include <linux/unistd.h>
>   #include <linux/kallsyms.h>
>   #include <linux/uaccess.h>
> +#include <linux/rcupdate.h>
>   
>   #include <asm/io.h>
>   #include <asm/asm-offsets.h>
> @@ -69,8 +70,10 @@ void cpu_idle(void)
>   
>   	/* endless idle loop with no priority at all */
>   	while (1) {
> +		rcu_idle_enter();
>   		while (!need_resched())
>   			barrier();
> +		rcu_idle_exit();
>   		schedule_preempt_disabled();
>   		check_pgt_cache();
>   	}

Builds and boots fine on parisc.
Acked-by: John David Anglin<dave.anglin@...l.net>

Dave

-- 
John David Anglin    dave.anglin@...l.net

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