shift and clocksource

shift and clocksource

[Carlo Caione]

Hi,
I was looking in the sources for time keeping. Why the shift field of the clocksource structure is always set to 10?
Also using the clocks_calc_mult_shift() in kernel sources I obtain different values for the shift variable.

Best regards,

--
Carlo Caione

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Re: shift and clocksource

[Sascha Hauer]

Hi Carlo,

On Sun, Jun 19, 2011 at 06:18:44PM +0200, Carlo Caione wrote:
> Hi,
> I was looking in the sources for time keeping. Why the shift field of
> the clocksource structure is always set to 10?  Also using the
> clocks_calc_mult_shift() in kernel sources I obtain different values
> for the shift variable.

The value 10 is copied from the initial clocksource. We should add
clocks_calc_mult_shift() to barebox and use it there also.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
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[PATCH] shift and clocksource

[Carlo Caione]

Added clocks_calc_mult_shift()

Signed-off-by: Carlo Caione <carlo.caione@gmail.com>
---
common/clock.c |   55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 55 insertions(+), 0 deletions(-)

diff --git a/common/clock.c b/common/clock.c
index 15df0ab..79c06c8 100644
--- a/common/clock.c
+++ b/common/clock.c
@@ -57,6 +57,61 @@ uint64_t get_time_ns(void)
EXPORT_SYMBOL(get_time_ns);

/**
+ * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
+ * @mult:       pointer to mult variable
+ * @shift:      pointer to shift variable
+ * @from:       frequency to convert from
+ * @to:         frequency to convert to
+ * @maxsec:     guaranteed runtime conversion range in seconds
+ *
+ * The function evaluates the shift/mult pair for the scaled math
+ * operations of clocksources and clockevents.
+ *
+ * @to and @from are frequency values in HZ. For clock sources @to is
+ * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
+ * event @to is the counter frequency and @from is NSEC_PER_SEC.
+ *
+ * The @maxsec conversion range argument controls the time frame in
+ * seconds which must be covered by the runtime conversion with the
+ * calculated mult and shift factors. This guarantees that no 64bit
+ * overflow happens when the input value of the conversion is
+ * multiplied with the calculated mult factor. Larger ranges may
+ * reduce the conversion accuracy by chosing smaller mult and shift
+ * factors.
+ */
+
+void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec)
+{
+        uint64_t tmp;
+        uint32_t sft, sftacc = 32;
+
+        /*
+         * Calculate the shift factor which is limiting the conversion
+         * range:
+         */
+        tmp = ((uint64_t)maxsec * from) >> 32;
+        while (tmp) {
+                tmp >>=1;
+                sftacc--;
+        }
+
+        /*
+         * Find the conversion shift/mult pair which has the best
+         * accuracy and fits the maxsec conversion range:
+         */
+        for (sft = 32; sft > 0; sft--) {
+                tmp = (uint64_t) to << sft;
+                tmp += from / 2;
+                do_div(tmp, from);
+                if ((tmp >> sftacc) == 0)
+                        break;
+        }
+        *mult = tmp;
+        *shift = sft;
+}
+
+
+/**
 * clocksource_hz2mult - calculates mult from hz and shift
 * @hz:                 Clocksource frequency in Hz
 * @shift_constant:     Clocksource shift factor
-- 
1.7.5.2


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Re: [PATCH] shift and clocksource

[Sascha Hauer]

On Tue, Jun 21, 2011 at 12:08:00AM +0200, Carlo Caione wrote:
> Added clocks_calc_mult_shift()
> 
> Signed-off-by: Carlo Caione <carlo.caione@gmail.com>
> ---
> common/clock.c |   55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++

You should also add this to include/clock.h. Otherwise the patch looks
good.

Sascha

> 1 files changed, 55 insertions(+), 0 deletions(-)
> 
> diff --git a/common/clock.c b/common/clock.c
> index 15df0ab..79c06c8 100644
> --- a/common/clock.c
> +++ b/common/clock.c
> @@ -57,6 +57,61 @@ uint64_t get_time_ns(void)
> EXPORT_SYMBOL(get_time_ns);
> 
> /**
> + * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
> + * @mult:       pointer to mult variable
> + * @shift:      pointer to shift variable
> + * @from:       frequency to convert from
> + * @to:         frequency to convert to
> + * @maxsec:     guaranteed runtime conversion range in seconds
> + *
> + * The function evaluates the shift/mult pair for the scaled math
> + * operations of clocksources and clockevents.
> + *
> + * @to and @from are frequency values in HZ. For clock sources @to is
> + * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
> + * event @to is the counter frequency and @from is NSEC_PER_SEC.
> + *
> + * The @maxsec conversion range argument controls the time frame in
> + * seconds which must be covered by the runtime conversion with the
> + * calculated mult and shift factors. This guarantees that no 64bit
> + * overflow happens when the input value of the conversion is
> + * multiplied with the calculated mult factor. Larger ranges may
> + * reduce the conversion accuracy by chosing smaller mult and shift
> + * factors.
> + */
> +
> +void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec)
> +{
> +        uint64_t tmp;
> +        uint32_t sft, sftacc = 32;
> +
> +        /*
> +         * Calculate the shift factor which is limiting the conversion
> +         * range:
> +         */
> +        tmp = ((uint64_t)maxsec * from) >> 32;
> +        while (tmp) {
> +                tmp >>=1;
> +                sftacc--;
> +        }
> +
> +        /*
> +         * Find the conversion shift/mult pair which has the best
> +         * accuracy and fits the maxsec conversion range:
> +         */
> +        for (sft = 32; sft > 0; sft--) {
> +                tmp = (uint64_t) to << sft;
> +                tmp += from / 2;
> +                do_div(tmp, from);
> +                if ((tmp >> sftacc) == 0)
> +                        break;
> +        }
> +        *mult = tmp;
> +        *shift = sft;
> +}
> +
> +
> +/**
>  * clocksource_hz2mult - calculates mult from hz and shift
>  * @hz:                 Clocksource frequency in Hz
>  * @shift_constant:     Clocksource shift factor
> -- 
> 1.7.5.2
> 
> 

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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Re: [PATCH] shift and clocksource

[Carlo Caione]

Added clocks_calc_mult_shift()

Signed-off-by: Carlo Caione <carlo.caione@gmail.com>
---
 common/clock.c  |   55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/clock.h |    2 ++
 2 files changed, 57 insertions(+), 0 deletions(-)

diff --git a/common/clock.c b/common/clock.c
index 15df0ab..79c06c8 100644
--- a/common/clock.c
+++ b/common/clock.c
@@ -57,6 +57,61 @@ uint64_t get_time_ns(void)
 EXPORT_SYMBOL(get_time_ns);
 
 /**
+ * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
+ * @mult:       pointer to mult variable
+ * @shift:      pointer to shift variable
+ * @from:       frequency to convert from
+ * @to:         frequency to convert to
+ * @maxsec:     guaranteed runtime conversion range in seconds
+ *
+ * The function evaluates the shift/mult pair for the scaled math
+ * operations of clocksources and clockevents.
+ *
+ * @to and @from are frequency values in HZ. For clock sources @to is
+ * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
+ * event @to is the counter frequency and @from is NSEC_PER_SEC.
+ *
+ * The @maxsec conversion range argument controls the time frame in
+ * seconds which must be covered by the runtime conversion with the
+ * calculated mult and shift factors. This guarantees that no 64bit
+ * overflow happens when the input value of the conversion is
+ * multiplied with the calculated mult factor. Larger ranges may
+ * reduce the conversion accuracy by chosing smaller mult and shift
+ * factors.
+ */
+
+void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec)
+{
+        uint64_t tmp;
+        uint32_t sft, sftacc = 32;
+
+        /*
+         * Calculate the shift factor which is limiting the conversion
+         * range:
+         */
+        tmp = ((uint64_t)maxsec * from) >> 32;
+        while (tmp) {
+                tmp >>=1;
+                sftacc--;
+        }
+
+        /*
+         * Find the conversion shift/mult pair which has the best
+         * accuracy and fits the maxsec conversion range:
+         */
+        for (sft = 32; sft > 0; sft--) {
+                tmp = (uint64_t) to << sft;
+                tmp += from / 2;
+                do_div(tmp, from);
+                if ((tmp >> sftacc) == 0)
+                        break;
+        }
+        *mult = tmp;
+        *shift = sft;
+}
+
+
+/**
  * clocksource_hz2mult - calculates mult from hz and shift
  * @hz:                 Clocksource frequency in Hz
  * @shift_constant:     Clocksource shift factor
diff --git a/include/clock.h b/include/clock.h
index b9acdb9..af5b939 100644
--- a/include/clock.h
+++ b/include/clock.h
@@ -25,6 +25,8 @@ int init_clock(struct clocksource *);
 
 uint64_t get_time_ns(void);
 
+void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec);
+
 uint32_t clocksource_hz2mult(uint32_t hz, uint32_t shift_constant);
 
 int is_timeout(uint64_t start_ns, uint64_t time_offset_ns);
-- 
1.7.5.2






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Re: [PATCH] shift and clocksource

[Sascha Hauer]

On Tue, Jun 21, 2011 at 08:56:53PM +0200, Carlo Caione wrote:
> Added clocks_calc_mult_shift()
> 
> Signed-off-by: Carlo Caione <carlo.caione@gmail.com>

Applied to -next

Sascha

> ---
>  common/clock.c  |   55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/clock.h |    2 ++
>  2 files changed, 57 insertions(+), 0 deletions(-)
> 
> diff --git a/common/clock.c b/common/clock.c
> index 15df0ab..79c06c8 100644
> --- a/common/clock.c
> +++ b/common/clock.c
> @@ -57,6 +57,61 @@ uint64_t get_time_ns(void)
>  EXPORT_SYMBOL(get_time_ns);
>  
>  /**
> + * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
> + * @mult:       pointer to mult variable
> + * @shift:      pointer to shift variable
> + * @from:       frequency to convert from
> + * @to:         frequency to convert to
> + * @maxsec:     guaranteed runtime conversion range in seconds
> + *
> + * The function evaluates the shift/mult pair for the scaled math
> + * operations of clocksources and clockevents.
> + *
> + * @to and @from are frequency values in HZ. For clock sources @to is
> + * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
> + * event @to is the counter frequency and @from is NSEC_PER_SEC.
> + *
> + * The @maxsec conversion range argument controls the time frame in
> + * seconds which must be covered by the runtime conversion with the
> + * calculated mult and shift factors. This guarantees that no 64bit
> + * overflow happens when the input value of the conversion is
> + * multiplied with the calculated mult factor. Larger ranges may
> + * reduce the conversion accuracy by chosing smaller mult and shift
> + * factors.
> + */
> +
> +void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec)
> +{
> +        uint64_t tmp;
> +        uint32_t sft, sftacc = 32;
> +
> +        /*
> +         * Calculate the shift factor which is limiting the conversion
> +         * range:
> +         */
> +        tmp = ((uint64_t)maxsec * from) >> 32;
> +        while (tmp) {
> +                tmp >>=1;
> +                sftacc--;
> +        }
> +
> +        /*
> +         * Find the conversion shift/mult pair which has the best
> +         * accuracy and fits the maxsec conversion range:
> +         */
> +        for (sft = 32; sft > 0; sft--) {
> +                tmp = (uint64_t) to << sft;
> +                tmp += from / 2;
> +                do_div(tmp, from);
> +                if ((tmp >> sftacc) == 0)
> +                        break;
> +        }
> +        *mult = tmp;
> +        *shift = sft;
> +}
> +
> +
> +/**
>   * clocksource_hz2mult - calculates mult from hz and shift
>   * @hz:                 Clocksource frequency in Hz
>   * @shift_constant:     Clocksource shift factor
> diff --git a/include/clock.h b/include/clock.h
> index b9acdb9..af5b939 100644
> --- a/include/clock.h
> +++ b/include/clock.h
> @@ -25,6 +25,8 @@ int init_clock(struct clocksource *);
>  
>  uint64_t get_time_ns(void);
>  
> +void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec);
> +
>  uint32_t clocksource_hz2mult(uint32_t hz, uint32_t shift_constant);
>  
>  int is_timeout(uint64_t start_ns, uint64_t time_offset_ns);
> -- 
> 1.7.5.2
> 
> 
> 
> 
> 
> 

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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