[PATCH 1/1] ARM: imx: Add sched_clock support to i.mx platform

[PATCH 1/1] ARM: imx: Add sched_clock support to i.mx platform

[Frank Li]

From: Xinyu Chen <xinyu.chen@freescale.com>

Add sched_clock() implement for i.mx platform to support nanosecond
resolution time for sched clock used by scheduler.

Signed-off-by: Xinyu Chen <xinyu.chen@freescale.com>
Signed-off-by: Frank Li <Frank.Li@freescale.com>
---
 arch/arm/plat-mxc/time.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/arch/arm/plat-mxc/time.c b/arch/arm/plat-mxc/time.c
index 9f0c261..de8a04f 100644
--- a/arch/arm/plat-mxc/time.c
+++ b/arch/arm/plat-mxc/time.c
@@ -123,6 +123,15 @@ static struct clocksource clocksource_mxc = {
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+unsigned long long sched_clock(void)
+{
+	if (!timer_base)
+		return 0;
+
+	return clocksource_cyc2ns(clocksource_mxc.read(&clocksource_mxc),
+			clocksource_mxc.mult, clocksource_mxc.shift);
+}
+
 static int __init mxc_clocksource_init(struct clk *timer_clk)
 {
 	unsigned int c = clk_get_rate(timer_clk);
-- 
1.7.1

[PATCH 1/1] ARM: imx: Add sched_clock support to i.mx platform

[Jamie Iles]

Hi,

On Wed, Mar 30, 2011 at 04:07:51PM +0800, Frank Li wrote:
> From: Xinyu Chen <xinyu.chen@freescale.com>
> 
> Add sched_clock() implement for i.mx platform to support nanosecond
> resolution time for sched clock used by scheduler.
> 
> Signed-off-by: Xinyu Chen <xinyu.chen@freescale.com>
> Signed-off-by: Frank Li <Frank.Li@freescale.com>
> ---
>  arch/arm/plat-mxc/time.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/plat-mxc/time.c b/arch/arm/plat-mxc/time.c
> index 9f0c261..de8a04f 100644
> --- a/arch/arm/plat-mxc/time.c
> +++ b/arch/arm/plat-mxc/time.c
> @@ -123,6 +123,15 @@ static struct clocksource clocksource_mxc = {
>  	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
>  };
>  
> +unsigned long long sched_clock(void)
> +{
> +	if (!timer_base)
> +		return 0;
> +
> +	return clocksource_cyc2ns(clocksource_mxc.read(&clocksource_mxc),
> +			clocksource_mxc.mult, clocksource_mxc.shift);
> +}

sched_clock() should be marked "notrace".  Also, this should use the 
sched_clock support in arch/arm/include/asm/sched_clock.h that takes 
care of wrapping and making it monotonic.

Jamie

[PATCH 1/1] ARM: imx: Add sched_clock support to i.mx platform

[Uwe Kleine-König]

On Wed, Mar 30, 2011 at 04:07:51PM +0800, Frank Li wrote:
> From: Xinyu Chen <xinyu.chen@freescale.com>
> 
> Add sched_clock() implement for i.mx platform to support nanosecond
> resolution time for sched clock used by scheduler.
> 
> Signed-off-by: Xinyu Chen <xinyu.chen@freescale.com>
> Signed-off-by: Frank Li <Frank.Li@freescale.com>
Some time ago Jan Weitzel sent a series with the same intention, but
Jan's patches look a bit more robust.

See http://thread.gmane.org/gmane.linux.ports.arm.kernel/110748

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

[PATCH 1/1] ARM: imx: Add sched_clock support to i.mx platform

[Russell King - ARM Linux]

On Wed, Mar 30, 2011 at 04:07:51PM +0800, Frank Li wrote:
> From: Xinyu Chen <xinyu.chen@freescale.com>
> 
> Add sched_clock() implement for i.mx platform to support nanosecond
> resolution time for sched clock used by scheduler.

NAK.

> diff --git a/arch/arm/plat-mxc/time.c b/arch/arm/plat-mxc/time.c
> index 9f0c261..de8a04f 100644
> --- a/arch/arm/plat-mxc/time.c
> +++ b/arch/arm/plat-mxc/time.c
> @@ -123,6 +123,15 @@ static struct clocksource clocksource_mxc = {
>  	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
>  };
>  
> +unsigned long long sched_clock(void)
> +{
> +	if (!timer_base)
> +		return 0;
> +
> +	return clocksource_cyc2ns(clocksource_mxc.read(&clocksource_mxc),
> +			clocksource_mxc.mult, clocksource_mxc.shift);
> +}

This is buggy because it won't scale to the full 64-bit value which
sched_clock() requires.  Please use the sched_clock() support I have
provided which ensures that a 32-bit counter is properly extended to
a full 64-bit value for sched_clock() - see arch/arm/kernel/sched_clock.c
and arch/arm/include/asm/sched_clock.h.