Subject: Re: [PATCH 6/9] PPC: remove redundant cpuidle_idle_call()

From: Preeti U Murthy <[email-masked]>
Date: Mon, 27 Jan 2014 17:29:51 +0530

Hi Nicolas,

On 01/27/2014 11:38 AM, Nicolas Pitre wrote:
> The core idle loop now takes care of it.  However a few things need
> checking:
> 
> - Invocation of cpuidle_idle_call() in pseries_lpar_idle() happened
>   through arch_cpu_idle() and was therefore always preceded by a call
>   to ppc64_runlatch_off().  To preserve this property now that
>   cpuidle_idle_call() is invoked directly from core code, a call to
>   ppc64_runlatch_off() has been added to idle_loop_prolog() in
>   platforms/pseries/processor_idle.c.
> 
> - Similarly, cpuidle_idle_call() was followed by ppc64_runlatch_off()
>   so a call to the later has been added to idle_loop_epilog().
> 
> - And since arch_cpu_idle() always made sure to re-enable IRQs if they
>   were not enabled, this is now
>   done in idle_loop_epilog() as well.
> 
> The above was made in order to keep the execution flow close to the
> original.  I don't know if that was strictly necessary. Someone well
> aquainted with the platform details might find some room for possible
> optimizations.
> 
> Signed-off-by: Nicolas Pitre <[email-masked]>
> ---
>  arch/powerpc/platforms/pseries/processor_idle.c |  5 ++++
>  arch/powerpc/platforms/pseries/setup.c          | 34 ++++++++++---------------
>  2 files changed, 19 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c
> index a166e38bd6..72ddfe3d2f 100644
> --- a/arch/powerpc/platforms/pseries/processor_idle.c
> +++ b/arch/powerpc/platforms/pseries/processor_idle.c
> @@ -33,6 +33,7 @@ static struct cpuidle_state *cpuidle_state_table;
> 
>  static inline void idle_loop_prolog(unsigned long *in_purr)
>  {
> +	ppc64_runlatch_off();
>  	*in_purr = mfspr(SPRN_PURR);
>  	/*
>  	 * Indicate to the HV that we are idle. Now would be
> @@ -49,6 +50,10 @@ static inline void idle_loop_epilog(unsigned long in_purr)
>  	wait_cycles += mfspr(SPRN_PURR) - in_purr;
>  	get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles);
>  	get_lppaca()->idle = 0;
> +
> +	if (irqs_disabled())
> +		local_irq_enable();
> +	ppc64_runlatch_on();
>  }
> 
>  static int snooze_loop(struct cpuidle_device *dev,
> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
> index c1f1908587..7604c19d54 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -39,7 +39,6 @@
>  #include <linux/irq.h>
>  #include <linux/seq_file.h>
>  #include <linux/root_dev.h>
> -#include <linux/cpuidle.h>
>  #include <linux/of.h>
>  #include <linux/kexec.h>
> 
> @@ -356,29 +355,24 @@ early_initcall(alloc_dispatch_log_kmem_cache);
> 
>  static void pseries_lpar_idle(void)
>  {
> -	/* This would call on the cpuidle framework, and the back-end pseries
> -	 * driver to  go to idle states
> +	/*
> +	 * Default handler to go into low thread priority and possibly
> +	 * low power mode by cedeing processor to hypervisor
>  	 */
> -	if (cpuidle_idle_call()) {
> -		/* On error, execute default handler
> -		 * to go into low thread priority and possibly
> -		 * low power mode by cedeing processor to hypervisor
> -		 */
> 
> -		/* Indicate to hypervisor that we are idle. */
> -		get_lppaca()->idle = 1;
> +	/* Indicate to hypervisor that we are idle. */
> +	get_lppaca()->idle = 1;
> 
> -		/*
> -		 * Yield the processor to the hypervisor.  We return if
> -		 * an external interrupt occurs (which are driven prior
> -		 * to returning here) or if a prod occurs from another
> -		 * processor. When returning here, external interrupts
> -		 * are enabled.
> -		 */
> -		cede_processor();
> +	/*
> +	 * Yield the processor to the hypervisor.  We return if
> +	 * an external interrupt occurs (which are driven prior
> +	 * to returning here) or if a prod occurs from another
> +	 * processor. When returning here, external interrupts
> +	 * are enabled.
> +	 */
> +	cede_processor();
> 
> -		get_lppaca()->idle = 0;
> -	}
> +	get_lppaca()->idle = 0;
>  }
> 
>  /*
> 

Reviewed-by: Preeti U Murthy <[email-masked]>

The consequence of this would be for other Power platforms like PowerNV,
we will need to invoke ppc_runlatch_off() and ppc_runlatch_on() in each
of the idle routines since the idle_loop_prologue() and
idle_loop_epilogue() are not invoked by them, but we will take care of this.

Regards
Preeti U Murthy