Re: [PATCH 8/7] cpufreq: make the iowait-is-busy-time a sysfs tunable

[Pavel Machek <pavel@ucw.cz>]

On Mon 2010-05-03 20:48:18, Arjan van de Ven wrote:
> On Tue, 27 Apr 2010 13:39:34 +0200
> Thomas Renninger <trenn@suse.de> wrote:
> 
> > On Friday 23 April 2010 06:08:19 pm Arjan van de Ven wrote:
> > > On Fri, 23 Apr 2010 10:50:10 +0200
> > > Thomas Renninger <trenn@suse.de> wrote:
> > >  Especially on battery, users will appreciate some minutes
> > >
> > > > of more battery lifetime and do not care about some ms of IO
> > > > latencies.
> > >
> > > the assumption that power doesn't matter on AC is a huge fiction
> > > that any data center operator would love to get out of everyones
> > > head as quickly as possible.
> > 
> > Have I said power doesn't matter on AC?
> > Do you agree that a datacenter has different performance vs power 
> > tradeoff demands as a battery driven mobile device?
> > 
> > Back to the topic:
> > As you did not answer on my (several) sysfs knob request(s), I expect
> > you agree with it and will add one.
> > 
> 
> yup it makes sense to have a sysfs knob with a sane default value
> 
> From: Arjan van de Ven <arjan@linux.intel.com>
> Subject: [PATCH] cpufreq: make the iowait-is-busy-time a sysfs tunable
> 
> Pavel Machek pointed out that not all CPUs have an efficient idle
> at high frequency. Specifically, older Intel and various AMD cpus
> would get a higher power usage when copying files from USB.
> 
> Mike Chan pointed out that the same is true for various ARM chips
> as well.
> 
> Thomas Renninger suggested to make this a sysfs tunable with a
> reasonable default.
> 
> This patch adds a sysfs tunable for the new behavior, and uses
> a very simple function to determine a reasonable default, depending
> on the CPU vendor/type.
> 
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

ACK.

> ---
>  drivers/cpufreq/cpufreq_ondemand.c |   46 +++++++++++++++++++++++++++++++++++-
>  1 files changed, 45 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
> index ed472f8..4877e8f 100644
> --- a/drivers/cpufreq/cpufreq_ondemand.c
> +++ b/drivers/cpufreq/cpufreq_ondemand.c
> @@ -109,6 +109,7 @@ static struct dbs_tuners {
>  	unsigned int down_differential;
>  	unsigned int ignore_nice;
>  	unsigned int powersave_bias;
> +	unsigned int io_is_busy;
>  } dbs_tuners_ins = {
>  	.up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
>  	.down_differential = DEF_FREQUENCY_DOWN_DIFFERENTIAL,
> @@ -260,6 +261,7 @@ static ssize_t show_##file_name						\
>  	return sprintf(buf, "%u\n", dbs_tuners_ins.object);		\
>  }
>  show_one(sampling_rate, sampling_rate);
> +show_one(io_is_busy, io_is_busy);
>  show_one(up_threshold, up_threshold);
>  show_one(ignore_nice_load, ignore_nice);
>  show_one(powersave_bias, powersave_bias);
> @@ -310,6 +312,22 @@ static ssize_t store_sampling_rate(struct kobject *a, struct attribute *b,
>  	return count;
>  }
>  
> +static ssize_t store_io_is_busy(struct kobject *a, struct attribute *b,
> +				   const char *buf, size_t count)
> +{
> +	unsigned int input;
> +	int ret;
> +	ret = sscanf(buf, "%u", &input);
> +	if (ret != 1)
> +		return -EINVAL;
> +
> +	mutex_lock(&dbs_mutex);
> +	dbs_tuners_ins.io_is_busy = !!input;
> +	mutex_unlock(&dbs_mutex);
> +
> +	return count;
> +}
> +
>  static ssize_t store_up_threshold(struct kobject *a, struct attribute *b,
>  				  const char *buf, size_t count)
>  {
> @@ -392,6 +410,7 @@ static struct global_attr _name = \
>  __ATTR(_name, 0644, show_##_name, store_##_name)
>  
>  define_one_rw(sampling_rate);
> +define_one_rw(io_is_busy);
>  define_one_rw(up_threshold);
>  define_one_rw(ignore_nice_load);
>  define_one_rw(powersave_bias);
> @@ -403,6 +422,7 @@ static struct attribute *dbs_attributes[] = {
>  	&up_threshold.attr,
>  	&ignore_nice_load.attr,
>  	&powersave_bias.attr,
> +	&io_is_busy.attr,
>  	NULL
>  };
>  
> @@ -527,7 +547,7 @@ static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)
>  		 * from the cpu idle time.
>  		 */
>  
> -		if (idle_time >= iowait_time)
> +		if (dbs_tuners_ins.io_is_busy && idle_time >= iowait_time)
>  			idle_time -= iowait_time;
>  
>  		if (unlikely(!wall_time || wall_time < idle_time))
> @@ -643,6 +663,29 @@ static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
>  	cancel_delayed_work_sync(&dbs_info->work);
>  }
>  
> +/*
> + * Not all CPUs want IO time to be accounted as busy; this depends on how
> + * efficient idling at a higher frequency/voltage is.
> + * Pavel Machek says this is not so for various generations of AMD and old
> + * Intel systems.
> + * Mike Chan (android.com) says this is also not true for ARM.
> + * Because of this, whitelist specific known (series) of CPUs by default, and
> + * leave all others up to the user.
> + */
> +static int should_io_be_busy(void)
> +{
> +#if defined(CONFIG_X86)
> +	/*
> +	 * For Intel, Core 2 (model 15) and later have an efficient idle.
> +	 */
> +	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
> +	    boot_cpu_data.x86 == 6 &&
> +	    boot_cpu_data.x86_model >= 15)
> +		return 1;
> +#endif
> +	return 0;
> +}
> +
>  static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
>  				   unsigned int event)
>  {
> @@ -705,6 +748,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
>  			dbs_tuners_ins.sampling_rate =
>  				max(min_sampling_rate,
>  				    latency * LATENCY_MULTIPLIER);
> +			dbs_tuners_ins.io_is_busy = should_io_be_busy();
>  		}
>  		mutex_unlock(&dbs_mutex);
>  

-- 
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