Re: cpuidle: Default y for pseries

On 01/12/2012 04:36 AM, Benjamin Herrenschmidt wrote:

On Wed, 2012-01-11 at 20:37 -0200, Thadeu Lima de Souza Cascardo wrote:

quoted

On Tue, Jan 10, 2012 at 03:05:35PM -0000, Benjamin Herrenschmidt wrote:

quoted

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 <benh@kernel.crashing.org>

---
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.

Ah ok. Well, making it built-in only makes sense anyway as I said
separately, so I think I'll just select it.

Cheers,
Ben.

quoted

  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.

quoted

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

The following patch disables pseries cpuidle driver to be loaded as a
module as there are build problems reported when one is trying to do so.
This is a work around for now until the problem is fixed.

arch/powerpc/platforms/pseries/Kconfig |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/Kconfig

b/arch/powerpc/platforms/pseries/Kconfig
index ae7b6d4..31f22c1 100644

--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig

@@ -122,7 +122,7 @@ config DTL
          Say N if you are unsure.

 config PSERIES_IDLE
-       tristate "Cpuidle driver for pSeries platforms"
+       bool "Cpuidle driver for pSeries platforms"
        depends on CPU_IDLE
        depends on PPC_PSERIES
        default y

As pointed out, 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),

Going forward, the aim is to remove the dependency of using these
functions from core power architecture functions. So I am proposing the
following changes:

a) Removing update_smt_snooze_delay () and allow the pseries
idle backend driver to query snooze entry on need basis
while initializing the driver fields by exporting an api to return
snooze value for a given cpu.

b) Replacing the pseries_notify_cpuidle_add_cpu() call
by registering a cpu_notifier to take actions accordingly.

Regards,
Deepthi