linux-kernel - Re: [PATCH V3 1/6] sched: idle: Add a weak arch_cpu_idle

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Date:	Sat, 08 Nov 2014 16:09:15 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>, rjw@...ysocki.net
CC:	nicolas.pitre@...aro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org, lenb@...nel.org
Subject: Re: [PATCH V3 1/6] sched: idle: Add a weak arch_cpu_idle_poll function

On 11/07/2014 08:01 PM, Daniel Lezcano wrote:
> The poll function is called when a timer expired or if we force to poll when
> the cpu_idle_force_poll option is set.
> 
> The poll function does:
> 
>        local_irq_enable();
>        while (!tif_need_resched())
>                cpu_relax();
> 
> This default poll function suits for the x86 arch because its rep; nop;
> hardware power optimization. But on other archs, this optimization does not
> exists and we are not saving power. The arch specific bits may want to
> optimize this loop by adding their own optimization.
> 
> Give an opportunity to the different platform to specify their own polling
> loop by adding a weak cpu_idle_poll_loop function.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  kernel/sched/idle.c | 29 +++++++++++++++++------------
>  1 file changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index c47fce7..ea65bbae 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -42,18 +42,6 @@ static int __init cpu_idle_nopoll_setup(char *__unused)
>  __setup("hlt", cpu_idle_nopoll_setup);
>  #endif
> 
> -static inline int cpu_idle_poll(void)
> -{
> -	rcu_idle_enter();
> -	trace_cpu_idle_rcuidle(0, smp_processor_id());
> -	local_irq_enable();
> -	while (!tif_need_resched())
> -		cpu_relax();
> -	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
> -	rcu_idle_exit();
> -	return 1;
> -}
> -
>  /* Weak implementations for optional arch specific functions */
>  void __weak arch_cpu_idle_prepare(void) { }
>  void __weak arch_cpu_idle_enter(void) { }
> @@ -65,6 +53,23 @@ void __weak arch_cpu_idle(void)
>  	local_irq_enable();
>  }
> 
> +void __weak arch_cpu_idle_poll(void)
> +{
> +	local_irq_enable();
> +	while (!tif_need_resched())
> +		cpu_relax();
> +}
> +
> +static inline int cpu_idle_poll(void)
> +{
> +	rcu_idle_enter();
> +	trace_cpu_idle_rcuidle(0, smp_processor_id());
> +	arch_cpu_idle_poll();
> +	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
> +	rcu_idle_exit();
> +	return 1;
> +}
> +
>  /**
>   * cpuidle_idle_call - the main idle function
>   *
> 

Thanks Daniel!

Reviewed-by: Preeti U. Murthy <preeti@...ux.vnet.ibm.com>

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