Re: [RFC PATCH V1 4/7] cpuidle: (powerpc) Add cpu_idle_wait() to allow switching idle routines

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2011-06-07 at 22:00 +0530, Trinabh Gupta wrote:

> diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
> index 39a2baa..932392b 100644
> --- a/arch/powerpc/kernel/idle.c
> +++ b/arch/powerpc/kernel/idle.c
> @@ -102,6 +102,24 @@ void cpu_idle(void)
>  	}
>  }
>  
> +static void do_nothing(void *unused)
> +{
> +}
> +
> +/*
> + * cpu_idle_wait - Used to ensure that all the CPUs come out of the old
> + * idle loop and start using the new idle loop.
> + * Required while changing idle handler on SMP systems.
> + * Caller must have changed idle handler to the new value before the call.
> + */
> +void cpu_idle_wait(void)
> +{
> +	smp_mb();
> +	/* kick all the CPUs so that they exit out of old idle routine */
> +	smp_call_function(do_nothing, NULL, 1);
> +}
> +EXPORT_SYMBOL_GPL(cpu_idle_wait);
> +
>  int powersave_nap;
>  
>  #ifdef CONFIG_SYSCTL

This is gross :-)

Do you need to absolutely ensure the idle task has changed or just
kicking it with a send reschedule is enough ?

Cheers,
Ben.