linux-kernel - Re: [PATCH 1/3] powercap, intel_rapl, implement get_max_time

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Date:	Thu, 17 Dec 2015 14:45:46 +0900
From:	Seiichi Ikarashi <s.ikarashi@...fujitsu.com>
To:	Prarit Bhargava <prarit@...hat.com>
CC:	<linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Radivoje Jovanovic <radivoje.jovanovic@...el.com>,
	Mathias Krause <minipli@...glemail.com>,
	Ajay Thomas <ajay.thomas.david.rajamanickam@...el.com>
Subject: Re: [PATCH 1/3] powercap, intel_rapl, implement get_max_time_window

On 2015-12-15 22:02, Prarit Bhargava wrote:
> The MSR_PKG_POWER_INFO register (Intel ASDM, section 14.9.3
> "Package RAPL Domain") provides a maximum time window which the
> system can support.  This window is read-only and is currently
> not examined when setting the time windows for the package.

I have been having a question here long time.
Maximum Time Window (bits 53:48) in MSR_PKG_POWER_INFO is only
6-bit length even though Time Window for Power Limit #1 (bits 23:17)
and Time Window for Power Limit #2 (bits 55:49) in MSR_PKG_POWER_LIMIT 
are both 7-bit length, not 6.

Do Intel guys have an answer for it?


The patch itself looks good to me.
Just minor comments below:

> diff --git a/drivers/powercap/intel_rapl.c b/drivers/powercap/intel_rapl.c
> index cc97f08..f765b2c 100644
> --- a/drivers/powercap/intel_rapl.c
> +++ b/drivers/powercap/intel_rapl.c
> @@ -493,13 +493,42 @@ static int get_current_power_limit(struct powercap_zone *power_zone, int id,
>  	return ret;
>  }
>  
> +static int get_max_time_window(struct powercap_zone *power_zone, int id,

The 2nd arg "id" is not necessary.

> +			       u64 *data)
> +{
> +	struct rapl_domain *rd;
> +	int ret = 0;
> +	u64 val;
> +
> +	get_online_cpus();
> +	rd = power_zone_to_rapl_domain(power_zone);
> +
> +	if (rapl_read_data_raw(rd, MAX_TIME_WINDOW, true, &val))

rapl_read_data_raw() can return -EINVAL and -ENODEV other than -EIO.

> +		ret = -EIO;

Is it OK to limit ret to -EIO here?

> +	else
> +		*data = val;
> +
> +	put_online_cpus();
> +	return ret;
> +}
> +
>  static int set_time_window(struct powercap_zone *power_zone, int id,
>  								u64 window)
>  {
>  	struct rapl_domain *rd;
>  	int ret = 0;
> +	u64 max_window;
>  
>  	get_online_cpus();
> +	ret = get_max_time_window(power_zone, id, &max_window);
> +	if (ret < 0)
> +		goto out;
> +
> +	if (window > max_window) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
>  	rd = power_zone_to_rapl_domain(power_zone);
>  	switch (rd->rpl[id].prim_id) {
>  	case PL1_ENABLE:
> @@ -511,6 +540,7 @@ static int set_time_window(struct powercap_zone *power_zone, int id,
>  	default:
>  		ret = -EINVAL;
>  	}
> +out:
>  	put_online_cpus();
>  	return ret;
>  }
> @@ -590,6 +620,7 @@ static struct powercap_zone_constraint_ops constraint_ops = {
>  	.set_time_window_us = set_time_window,
>  	.get_time_window_us = get_time_window,
>  	.get_max_power_uw = get_max_power,
> +	.get_max_time_window_us = get_max_time_window,
>  	.get_name = get_constraint_name,
>  };
>  
> diff --git a/drivers/powercap/powercap_sys.c b/drivers/powercap/powercap_sys.c
> index 84419af..7d77b83 100644
> --- a/drivers/powercap/powercap_sys.c
> +++ b/drivers/powercap/powercap_sys.c
> @@ -101,7 +101,7 @@ static ssize_t store_constraint_##_attr(struct device *dev,\
>  	int err; \
>  	u64 value; \
>  	struct powercap_zone *power_zone = to_powercap_zone(dev); \
> -	int id; \
> +	int id, ret; \
>  	struct powercap_zone_constraint *pconst;\
>  	\
>  	if (!sscanf(dev_attr->attr.name, "constraint_%d_", &id)) \
> @@ -113,8 +113,10 @@ static ssize_t store_constraint_##_attr(struct device *dev,\
>  	if (err) \
>  		return -EINVAL; \
>  	if (pconst && pconst->ops && pconst->ops->set_##_attr) { \
> -		if (!pconst->ops->set_##_attr(power_zone, id, value)) \
> +		ret = pconst->ops->set_##_attr(power_zone, id, value); \
> +		if (!ret) \
>  			return count; \
> +		return ret; \

An opposite question to above.
Is it OK not to limit the return value to -EINVAL here?
Do you want this function to return -EIO or something?

>  	} \
>  	\
>  	return -ENODATA; \
> 

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