Re: [PATCH 12/15] hwmon, fam15h_power: introduce a cpu accumulated power reporting algorithm

[Guenter Roeck <linux@roeck-us.net>]

On 08/30/2015 09:16 PM, Huang Rui wrote:
> On Fri, Aug 28, 2015 at 07:05:13AM -0700, Guenter Roeck wrote:
>> On 08/28/2015 03:45 AM, Huang Rui wrote:
>>> On Thu, Aug 27, 2015 at 10:30:43AM -0700, Guenter Roeck wrote:
>>>> On Thu, Aug 27, 2015 at 04:07:43PM +0800, Huang Rui wrote:
>>>>> This patch introduces an algorithm that computes the average power by
>>>>> reading a delta value of “core power accumulator” register during
>>>>> measurement interval, and then dividing delta value by the length of
>>>>> the time interval.
>>>>>
>>>>> User is able to use power1_acc entry to measure the processor power
>>>>> consumption and power1_acc just needs to be read twice with an needed
>>>>> interval in-between.
>>>>>
>>>>> A simple example:
>>>>>
>>>>> $ cat /sys/bus/pci/devices/0000\:00\:18.4/hwmon/hwmon0/power1_acc
>>>>> $ sleep 10000s
>>>>> $ cat /sys/bus/pci/devices/0000\:00\:18.4/hwmon/hwmon0/power1_acc
>>>>>
>>>>> The result is current average processor power consumption in 10000
>>>>> seconds. The unit of the result is uWatt.
>>>>>
>>>>> Signed-off-by: Huang Rui <ray.huang@amd.com>
>>>>> ---
>>>>>   drivers/hwmon/fam15h_power.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
>>>>>   1 file changed, 62 insertions(+)
>>>>>
>>>>> diff --git a/drivers/hwmon/fam15h_power.c b/drivers/hwmon/fam15h_power.c
>>>>> index d529e4b..3bab797 100644
>>>>> --- a/drivers/hwmon/fam15h_power.c
>>>>> +++ b/drivers/hwmon/fam15h_power.c
>>>>> @@ -60,6 +60,7 @@ struct fam15h_power_data {
>>>>>   	u64 cu_acc_power[MAX_CUS];
>>>>>   	/* performance timestamp counter */
>>>>>   	u64 cpu_sw_pwr_ptsc[MAX_CUS];
>>>>> +	struct mutex acc_pwr_mutex;
>>>>>   };
>>>>>
>>>>>   static ssize_t show_power(struct device *dev,
>>>>> @@ -121,17 +122,74 @@ static DEVICE_ATTR(power1_crit, S_IRUGO, show_power_crit, NULL);
>>>>>   static struct attribute_group fam15h_power_group;
>>>>>   __ATTRIBUTE_GROUPS(fam15h_power);
>>>>>
>>>>> +static ssize_t show_power_acc(struct device *dev,
>>>>> +			      struct device_attribute *attr, char *buf)
>>>>> +{
>>>>> +	int cpu, cu, cu_num, cores_per_cu;
>>>>> +	u64 curr_cu_acc_power[MAX_CUS],
>>>>> +	    curr_ptsc[MAX_CUS], jdelta[MAX_CUS];
>>>>> +	u64 tdelta, avg_acc;
>>>>> +	struct fam15h_power_data *data = dev_get_drvdata(dev);
>>>>> +
>>>>> +	cores_per_cu = amd_get_cores_per_cu();
>>>>> +	cu_num = boot_cpu_data.x86_max_cores / cores_per_cu;
>>>>> +
>>>>> +	for (cpu = 0, avg_acc = 0; cpu < cu_num * cores_per_cu; cpu += cores_per_cu) {
>>>>> +		cu = cpu / cores_per_cu;
>>>>> +		if (rdmsrl_safe_on_cpu(cpu, MSR_F15H_PTSC, &curr_ptsc[cu])) {
>>>>> +			pr_err("Failed to read PTSC counter MSR on core%d\n",
>>>>> +			       cpu);
>>>>> +			return 0;
>>>>> +		}
>>>>> +
>>>>> +		if (rdmsrl_safe_on_cpu(cpu, MSR_F15H_CU_PWR_ACCUMULATOR,
>>>>> +				       &curr_cu_acc_power[cu])) {
>>>>> +			pr_err("Failed to read compute unit power accumulator MSR on core%d\n",
>>>>> +			       cpu);
>>>>> +			return 0;
>>>>> +		}
>>>>> +
>>>>> +		if (curr_cu_acc_power[cu] < data->cu_acc_power[cu]) {
>>>>> +			jdelta[cu] = data->max_cu_acc_power + curr_cu_acc_power[cu];
>>>>> +			jdelta[cu] -= data->cu_acc_power[cu];
>>>>> +		} else {
>>>>> +			jdelta[cu] = curr_cu_acc_power[cu] - data->cu_acc_power[cu];
>>>>> +		}
>>>>> +		tdelta = curr_ptsc[cu] - data->cpu_sw_pwr_ptsc[cu];
>>>>> +		jdelta[cu] *= data->cpu_pwr_sample_ratio * 1000;
>>>>> +		do_div(jdelta[cu], tdelta);
>>>>> +
>>>>> +		mutex_lock(&data->acc_pwr_mutex);
>>>>> +		data->cu_acc_power[cu] = curr_cu_acc_power[cu];
>>>>> +		data->cpu_sw_pwr_ptsc[cu] = curr_ptsc[cu];
>>>>> +		mutex_unlock(&data->acc_pwr_mutex);
>>>>> +
>>>>> +		/* the unit is microWatt */
>>>>> +		avg_acc += jdelta[cu];
>>>>> +	}
>>>>> +
>>>>> +	return sprintf(buf, "%u\n", (unsigned int) avg_acc);
>>>>> +}
>>>>> +static DEVICE_ATTR(power1_acc, S_IRUGO, show_power_acc, NULL);
>>>>
>>>> I am not really a friend of introducing a non-standard attribute.
>>>> Does the energy attribute not work here ?
>>>>
>>>
>>> You're right. Non-standard attribute might not be good. Could you
>>> please give me some hints if I use "energy" instead?
>>>
>> 1 Joule = 1 Watt-second.
>>
>> Something else, though - did you make sure that your code doesn't overflow ?
>> Even though you calculate the average in an u64, you display it as unsigned.
>>
>
> Thanks to your reminder. It should not be overflow. The maximum power
> consumption of processor (AMD CZ and future 15h) is about 15 Watts =
> 15,000,000 uWatts = 0xE4E1C0 uWatts, the size is 24 < 32 < 64 bits.
>
> Actually, the unit of jdelta is not Joule. Because the tdelta is the
> loops (cycles) that PTSC counter (the freqency is about 100 MHz)
> counts not seconds.
>
> So avg_acc is the average power consumption not the accumulated energy.
>

Would power1_average then be better suitable for the attribute ?
There is also power1_average_interval which could be used to make
the interval configurable.

Thanks,
Guenter