Re: [patch 26/34] powerpc: Use generic idle loop

Deepthi Dharwar
2013-04-01T09:16:05Z

On 03/28/2013 09:10 PM, Srivatsa S. Bhat wrote:
> On 03/22/2013 03:23 AM, Thomas Gleixner wrote:
>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> ---
> [...]
>> Index: linux-2.6/arch/powerpc/kernel/idle.c
>> ===================================================================
>> --- linux-2.6.orig/arch/powerpc/kernel/idle.c
>> +++ linux-2.6/arch/powerpc/kernel/idle.c
>> @@ -50,64 +50,30 @@ static int __init powersave_off(char *ar
>> }
>> __setup("powersave=off", powersave_off);
>>
>> -/*
>> - * The body of the idle task.
>> - */
>> -void cpu_idle(void)
>> +void arch_cpu_idle(void)
>> {
>> - set_thread_flag(TIF_POLLING_NRFLAG);
>> - while (1) {
>> - tick_nohz_idle_enter();
>> - rcu_idle_enter();
>> -
>> - while (!need_resched() && !cpu_should_die()) {
>> - ppc64_runlatch_off();
>> -
>> - if (ppc_md.power_save) {
>> - clear_thread_flag(TIF_POLLING_NRFLAG);
>> - /*
>> - * smp_mb is so clearing of TIF_POLLING_NRFLAG
>> - * is ordered w.r.t. need_resched() test.
>> - */
>> - smp_mb();
>> - local_irq_disable();
>> -
>> - /* Don't trace irqs off for idle */
>> - stop_critical_timings();
>> -
>> - /* check again after disabling irqs */
>> - if (!need_resched() && !cpu_should_die())
>> - ppc_md.power_save();
>> -
>> - start_critical_timings();
>> -
>> - /* Some power_save functions return with
>> - * interrupts enabled, some don't.
>> - */
>> - if (irqs_disabled())
>> - local_irq_enable();
>> - set_thread_flag(TIF_POLLING_NRFLAG);
>> -
>> - } else {
>> - /*
>> - * Go into low thread priority and possibly
>> - * low power mode.
>> - */
>> - HMT_low();
>> - HMT_very_low();
>> - }
>> - }
>> -
>> - HMT_medium();
>> - ppc64_runlatch_on();
>> - rcu_idle_exit();
>> - tick_nohz_idle_exit();
>> - if (cpu_should_die()) {
>> - sched_preempt_enable_no_resched();
>> - cpu_die();
>> - }
>> - schedule_preempt_disabled();
>> + ppc64_runlatch_off();
>> +
>> + if (ppc_md.power_save) {
>> + ppc_md.power_save();
>> + /*
>> + * Some power_save functions return with
>> + * interrupts enabled, some don't.
>> + */
>> + if (irqs_disabled())
>> + local_irq_enable();
>> + } else {
>> + local_irq_enable();
>> + /*
>> + * Go into low thread priority and possibly
>> + * low power mode.
>> + */
>> + HMT_low();
>> + HMT_very_low();
>> }
>> +
>> + HMT_medium();
>> + ppc64_runlatch_on();
>> }
>>

The below patch is essential to get hotplug working on POWER.
With that, generic idle loop works fine for PSERIES.

Tested-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>

>
> The call to cpu_die() seems to be missing. And considering this commit,
>
> commit a7c2bb8279d20d853e43c34584eaf2b039de8026
> Author: Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
> Date: Wed Aug 4 18:28:33 2010 +0000
>
> powerpc: Re-enable preemption before cpu_die()
>
> we need to call it with preempt enabled. So how about folding the
> following diff with this patch?
>
>
> diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
> index b751baa..e434fb9 100644
> --- a/arch/powerpc/kernel/idle.c
> +++ b/arch/powerpc/kernel/idle.c
> @@ -33,11 +33,6 @@
> #include <asm/runlatch.h>
> #include <asm/smp.h>
>
> -#ifdef CONFIG_HOTPLUG_CPU
> -#define cpu_should_die() cpu_is_offline(smp_processor_id())
> -#else
> -#define cpu_should_die() 0
> -#endif
>
> unsigned long cpuidle_disable = IDLE_NO_OVERRIDE;
> EXPORT_SYMBOL(cpuidle_disable);
> @@ -50,6 +45,12 @@ static int __init powersave_off(char *arg)
> }
> __setup("powersave=off", powersave_off);
>
> +void arch_cpu_idle_dead(void)
> +{
> + sched_preempt_enable_no_resched();
> + cpu_die();
> +}
> +
> void arch_cpu_idle(void)
> {
> ppc64_runlatch_off();
>
>
> Regards,
> Srivatsa S. Bhat
>