Re: [PATCH V3 1/6] sched: idle: Add a weak arch_cpu_idle_poll function

Preeti U Murthy
2014-11-08T10:39:25Z

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@linaro.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@linux.vnet.ibm.com>