Subject: Re: cpuidle: Default y for pseries

From: Thadeu Lima de Souza Cascardo <[email-masked]>
Date: Wed, 11 Jan 2012 20:37:44 -0200

On Tue, Jan 10, 2012 at 03:05:35PM -0000, Benjamin Herrenschmidt wrote:
> We just replaced the pseries platform idle loops with a cpuidle backend,
> however that means that you won't get any power saving and won't return
> any unused idle time to the hypervisor unless cpuidle is enabled.
> 
> Thus is should default to y when pseries is enabled. I prefer that to
> a select so we can still make it modular if we want to.
> 
> Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
> 
> ---
> Linus, do you want to just pick that up or should I put it into powerpc.git
> and ask you to pull ? I will have 2 or 3 other fixes there later today,
> but I wanted to make sure you were ok with the approach with this
> specific one.

Hi, Ben.

Note that building with CONFIG_PSERIES_IDLE=m fails.

  CC [M]  arch/powerpc/platforms/pseries/processor_idle.o
arch/powerpc/platforms/pseries/processor_idle.c:35: error: redefinition
of ‘update_smt_snooze_delay’
/root/linux/arch/powerpc/include/asm/system.h:230: note: previous
definition of ‘update_smt_snooze_delay’ was here
arch/powerpc/platforms/pseries/processor_idle.c:175: error: redefinition
of ‘pseries_notify_cpuidle_add_cpu’
/root/linux/arch/powerpc/include/asm/system.h:231: note: previous
definition of ‘pseries_notify_cpuidle_add_cpu’ was here
make[2]: *** [arch/powerpc/platforms/pseries/processor_idle.o] Error 1
make[1]: *** [arch/powerpc/platforms/pseries] Error 2
make: *** [arch/powerpc/platforms] Error 2

asm/system.h has empty inline implementations for
update_smt_snooze_delay and pseries_notify_cpuidle_add_cpu, which are
used when CONFIG_PSERIES_IDLE is undefined. Since those two functions
are used in core power architecture functions (store_smt_snooze_delay
at kernel/sysfs.c and smp_xics_setup_cpu at platforms/pseries/smp.c),
this requires some rework in these interactions or we should simply
disable PSERIES_IDLE to be built as a module for now.

Regards.
Cascardo.

> 
> diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
> index 7dbc4a8..62ca70d 100644
> --- a/drivers/cpuidle/Kconfig
> +++ b/drivers/cpuidle/Kconfig
> @@ -1,7 +1,8 @@
>  
>  config CPU_IDLE
>  	bool "CPU idle PM support"
> -	default ACPI
> +	default y if ACPI
> +	default y if PPC_PSERIES
>  	help
>  	  CPU idle is a generic framework for supporting software-controlled
>  	  idle processor power management.  It includes modular cross-platform