[PATCH] TWD: enable one-shot mode

[PATCH] TWD: enable one-shot mode

[Russell King - ARM Linux]

Allow one shot timer mode to be used with the TWD.  This allows
NOHZ mode to be used on SMP systems using the TWD localtimer.

Tested on Versatile Express.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
Acks/Tested-by's would be appreciated, thanks.

Merry Christmas.

 arch/arm/Kconfig |    1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5634dce..4a6c4d7 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1282,6 +1282,7 @@ config HAVE_ARM_SCU
 config HAVE_ARM_TWD
 	bool
 	depends on SMP
+	select TICK_ONESHOT
 	help
 	  This options enables support for the ARM timer and watchdog unit
 

[PATCH] TWD: enable one-shot mode

[Linus Walleij]

2010/12/24 Russell King - ARM Linux <linux@arm.linux.org.uk>:
> Allow one shot timer mode to be used with the TWD. ?This allows
> NOHZ mode to be used on SMP systems using the TWD localtimer.
>
> Tested on Versatile Express.
>
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> ---
> Acks/Tested-by's would be appreciated, thanks.

Tested on the U8500 and doesn't seem to break anything...

Local interrupts after a few minutes of use before patching
(and enabling NO_HZ):
LOC:       8203       8224

After patching;
LOC:        233        322

Looks like it's working, too.

Tested-by: Linus Walleij <linus.walleij@stericsson.com>

Yours,
Linus Walleij

[PATCH] TWD: enable one-shot mode

[Stephen Boyd]

On 12/24/2010 11:18 AM, Russell King - ARM Linux wrote:
> Allow one shot timer mode to be used with the TWD.  This allows
> NOHZ mode to be used on SMP systems using the TWD localtimer.
>
> Tested on Versatile Express.
>
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> ---
> Acks/Tested-by's would be appreciated, thanks.
>

I see this patch was already tested and merged but can you elaborate on
why this was done? From what I understand, NOHZ selects one-shot (like
is done in this patch), so why don't the machines with a TWD choose NOHZ
or high res timers?

Putting it another way, if my machine supports a oneshot capable
clockevent device should I be selecting oneshot regardless of the NOHZ
and high res config option being chosen?

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

[PATCH] TWD: enable one-shot mode

[Russell King - ARM Linux]

On Mon, Jan 10, 2011 at 09:12:36PM -0800, Stephen Boyd wrote:
> On 12/24/2010 11:18 AM, Russell King - ARM Linux wrote:
> > Allow one shot timer mode to be used with the TWD.  This allows
> > NOHZ mode to be used on SMP systems using the TWD localtimer.
> >
> > Tested on Versatile Express.
> >
> > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> > ---
> > Acks/Tested-by's would be appreciated, thanks.
> >
> 
> I see this patch was already tested and merged but can you elaborate on
> why this was done? From what I understand, NOHZ selects one-shot (like
> is done in this patch), so why don't the machines with a TWD choose NOHZ
> or high res timers?

You're right - so it's not actually required.  It should probably be
reverted, though it does no damage...

[PATCH] TWD: enable one-shot mode

[Stephen Boyd]

On 01/11/2011 03:52 AM, Russell King - ARM Linux wrote:
> On Mon, Jan 10, 2011 at 09:12:36PM -0800, Stephen Boyd wrote:
>>
>> I see this patch was already tested and merged but can you elaborate on
>> why this was done? From what I understand, NOHZ selects one-shot (like
>> is done in this patch), so why don't the machines with a TWD choose NOHZ
>> or high res timers?
>
> You're right - so it's not actually required.  It should probably be
> reverted, though it does no damage...

Now I'm wondering why there are other 'select TICK_ONESHOT' lines in
arch/arm/Kconfig. Can we just remove them all? Otherwise it feels like
we're making it confusing for others later on.

----->8---[cut here]----8<-----
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index e2f8011..7750a78 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -532,7 +532,6 @@ config ARCH_MMP
        select CLKDEV_LOOKUP
        select GENERIC_CLOCKEVENTS
        select HAVE_SCHED_CLOCK
-       select TICK_ONESHOT
        select PLAT_PXA
        select SPARSE_IRQ
        help
@@ -613,7 +612,6 @@ config ARCH_PXA
        select ARCH_REQUIRE_GPIOLIB
        select GENERIC_CLOCKEVENTS
        select HAVE_SCHED_CLOCK
-       select TICK_ONESHOT
        select PLAT_PXA
        select SPARSE_IRQ
        help
@@ -668,7 +666,6 @@ config ARCH_SA1100
        select GENERIC_CLOCKEVENTS
        select HAVE_CLK
        select HAVE_SCHED_CLOCK
-       select TICK_ONESHOT
        select ARCH_REQUIRE_GPIOLIB
        help
          Support for StrongARM 11x0 based boards.
@@ -1300,7 +1297,6 @@ config HAVE_ARM_SCU
 config HAVE_ARM_TWD
        bool
        depends on SMP
-       select TICK_ONESHOT
        help
          This options enables support for the ARM timer and watchdog unit

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.