Re: [PATCH 3/7] CPUFREQ: ondemand/conservative: sanitizesampling_rate restrictions

[Andrew Morton]

On Tue,  3 Feb 2009 17:46:42 +0100 Thomas Renninger <trenn@xxxxxxx> wrote:

> Limit sampling rate to transition_latency * 100 or kernel limits.
> If sampling_rate is tried to be set too low, set the lowest allowed value.
> 
> Signed-off-by: Thomas Renninger <trenn@xxxxxxx>
> ---
>  Documentation/cpu-freq/governors.txt   |   14 +++++++++++++-
>  drivers/cpufreq/cpufreq_conservative.c |   19 ++++++++++++++++---
>  drivers/cpufreq/cpufreq_ondemand.c     |   19 +++++++++++++++----
>  3 files changed, 44 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt
> index 9b18512..ce73f3e 100644
> --- a/Documentation/cpu-freq/governors.txt
> +++ b/Documentation/cpu-freq/governors.txt
> @@ -117,7 +117,19 @@ accessible parameters:
>  sampling_rate: measured in uS (10^-6 seconds), this is how often you
>  want the kernel to look at the CPU usage and to make decisions on
>  what to do about the frequency.  Typically this is set to values of
> -around '10000' or more.
> +around '10000' or more. It's default value is (cmp. with users-guide.txt):
> +transition_latency * 1000
> +The lowest value you can set is:
> +transition_latency * 100 or it may get restricted to a value where it
> +makes not sense for the kernel anymore to poll that often which depends
> +on your HZ config variable (HZ=1000: max=20000us, HZ=250: max=5000).
> +Be aware that transition latency is in ns and sampling_rate is in us, so you
> +get the same sysfs value by default.
> +Sampling rate should always get adjusted considering the transition latency
> +To set the sampling rate 750 times as high as the transition latency
> +in the bash (as said, 1000 is default), do:
> +echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \
> +    >ondemand/sampling_rate
>  
>  show_sampling_rate_(min|max): THIS INTERFACE IS DEPRECATED, DON'T USE IT.
>  You can use wider ranges now and the general
> diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
> index 5ba0a3f..b8bbd4a 100644
> --- a/drivers/cpufreq/cpufreq_conservative.c
> +++ b/drivers/cpufreq/cpufreq_conservative.c
> @@ -54,7 +54,18 @@ static unsigned int def_sampling_rate;
>  			(MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
>  #define MIN_SAMPLING_RATE			\
>  			(def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
> +/* Above MIN_SAMPLING_RATE will vanish with its sysfs file soon
> + * Define the minimal settable sampling rate to the greater of:
> + *   - "HW transition latency" * 100 (same as default sampling / 10)
> + *   - MIN_STAT_SAMPLING_RATE
> + * To avoid that userspace shoots itself.
> +*/
> +#define MINIMUM_SAMPLING_RATE			\
> +			((def_sampling_rate / 10) < MIN_STAT_SAMPLING_RATE \
> +			 ? MIN_STAT_SAMPLING_RATE : (def_sampling_rate / 10))

Use
	max(def_sampling_rate / 10, MIN_STAT_SAMPLING_RATE)
?

But really, this should be a plain old C function.  Hiding a bunch of C
code inside a macro which purports to be a compile-time constant is rude.

> +/* This will also vanish soon with removing sampling_rate_max */
>  #define MAX_SAMPLING_RATE			(500 * def_sampling_rate)

Ditto, really.

> +
>  #define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER	(1000)
>  #define DEF_SAMPLING_DOWN_FACTOR		(1)
>  #define MAX_SAMPLING_DOWN_FACTOR		(10)
> @@ -197,12 +208,14 @@ static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
>  	ret = sscanf (buf, "%u", &input);
>  
>  	mutex_lock(&dbs_mutex);
> -	if (ret != 1 || input > MAX_SAMPLING_RATE || input < MIN_SAMPLING_RATE) {
> +	if (ret != 1) {
>  		mutex_unlock(&dbs_mutex);
>  		return -EINVAL;
>  	}
> -
> -	dbs_tuners_ins.sampling_rate = input;
> +	if  (input < MINIMUM_SAMPLING_RATE)
> +		dbs_tuners_ins.sampling_rate = MINIMUM_SAMPLING_RATE;
> +	else
> +		dbs_tuners_ins.sampling_rate = input;

	dbs_tuners_ins.sampling_rate = max(MINIMUM_SAMPLING_RATE, input);

>  	mutex_unlock(&dbs_mutex);
>  
>  	return count;
> diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
> index 4b42e36..70e0841 100644
> --- a/drivers/cpufreq/cpufreq_ondemand.c
> +++ b/drivers/cpufreq/cpufreq_ondemand.c
> @@ -52,6 +52,16 @@ static unsigned int def_sampling_rate;
>  			(MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
>  #define MIN_SAMPLING_RATE			\
>  			(def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
> +/* Above MIN_SAMPLING_RATE will vanish with its sysfs file soon
> + * Define the minimal settable sampling rate to the greater of:
> + *   - "HW transition latency" * 100 (same as default sampling / 10)
> + *   - MIN_STAT_SAMPLING_RATE
> + * To avoid that userspace shoots itself.
> +*/
> +#define MINIMUM_SAMPLING_RATE			\
> +			((def_sampling_rate / 10) < MIN_STAT_SAMPLING_RATE \
> +			 ? MIN_STAT_SAMPLING_RATE : (def_sampling_rate / 10))
> +/* This will also vanish soon with removing sampling_rate_max */
>  #define MAX_SAMPLING_RATE			(500 * def_sampling_rate)
>  #define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER	(1000)
>  #define TRANSITION_LATENCY_LIMIT		(10 * 1000 * 1000)
> @@ -243,13 +253,14 @@ static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
>  	ret = sscanf(buf, "%u", &input);
>  
>  	mutex_lock(&dbs_mutex);
> -	if (ret != 1 || input > MAX_SAMPLING_RATE
> -		     || input < MIN_SAMPLING_RATE) {
> +	if (ret != 1) {
>  		mutex_unlock(&dbs_mutex);
>  		return -EINVAL;
>  	}
> -
> -	dbs_tuners_ins.sampling_rate = input;
> +	if  (input < MINIMUM_SAMPLING_RATE)
> +		dbs_tuners_ins.sampling_rate = MINIMUM_SAMPLING_RATE;
> +	else
> +		dbs_tuners_ins.sampling_rate = input;
>  	mutex_unlock(&dbs_mutex);

etceterata.
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