Re: [PATCH v2 3/4] lib/power: add get and set API for scaling freq min and max with pstate mode

[Kevin Laatz <kevin.laatz@intel.com>]

On 18/05/2022 10:05, Burakov, Anatoly wrote:
> On 19-Apr-22 12:25 PM, Kevin Laatz wrote:
>> Add new get/set API to allow the user or application to set the minimum
>> and maximum frequencies to use when scaling.
>> Previously, the frequency range was determined by the HW capabilities of
>> the CPU. With this new API, the user or application can constrain this
>> if required.
>>
>> Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
>> ---
>
> <snip>
>
>>   +int
>> +rte_power_pmd_mgmt_set_scaling_freq_min(unsigned int lcore, unsigned 
>> int min)
>> +{
>> +    if (lcore >= RTE_MAX_LCORE) {
>> +        RTE_LOG(ERR, POWER, "Invalid lcore ID: %u\n", lcore);
>> +        rte_errno = EINVAL;
>> +        return -1;
>> +    }
>> +    scale_freq_min[lcore] = min;
>
> Are there any constraints on the value ranges, or are we just going to 
> accept any and all values? If the idea was to allow valid values plus 
> some special "default" value, you can still restrict the range, but 
> allow 0 as a special case?

When writing min/max values to HW the values are clamped. Since the API 
takes unsigned integer for the frequency value (in this case 'min'), any 
value can be considered as 'valid'.

That being said, this should at least check that min <= max for the same 
lcore. I'll add this for v3.


>
>> +
>> +    return 0;
>> +}
>> +
>> +int
>> +rte_power_pmd_mgmt_set_scaling_freq_max(unsigned int lcore, unsigned 
>> int max)
>> +{
>> +    if (lcore >= RTE_MAX_LCORE) {
>> +        RTE_LOG(ERR, POWER, "Invalid lcore ID: %u\n", lcore);
>> +        rte_errno = EINVAL;
>> +        return -1;
>> +    }
>> +    scale_freq_max[lcore] = max;
>
> Same as above. Also, do we want UINT32_MAX be the "special" value for 
> the "max" case? What do you think of having "0" as "not set", but 
> maybe set it internally to UINT32_MAX if you still want to keep using 
> the RTE_MIN/MAX macros?

Similar to  'set_scaling_freq_min', the value will be clamped by HW so 
any value can be considered 'valid'. I don't see the benefit of having 
"0" for not set, since UINT32_MAX will achieve the same result, i.e. the 
value won't be used (it will fall back the max value in sysfs). Do you 
have a use-case for it if we don't need a 'special case'?

Will add a check to make sure max >= min for v3.


>
>> +
>> +    return 0;
>> +}
>> +
>> +int
>> +rte_power_pmd_mgmt_get_scaling_freq_min(unsigned int lcore)
>> +{
>
> <snip>
>
>> diff --git a/lib/power/rte_power_pmd_mgmt.h 
>> b/lib/power/rte_power_pmd_mgmt.h
>> index 18a9c3abb5..74e3fa710b 100644
>> --- a/lib/power/rte_power_pmd_mgmt.h
>> +++ b/lib/power/rte_power_pmd_mgmt.h
>> @@ -148,6 +148,86 @@ __rte_experimental
>>   unsigned int
>>   rte_power_pmd_mgmt_get_pause_duration(void);
>>   +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change, or be removed, without 
>> prior notice.
>> + *
>> + * Set the min frequency to be used for frequency scaling.
>> + *
>> + * @note Supported by: Pstate mode.
>> + *
>> + * @param lcore
>> + *   The ID of the lcore to set the min frequency for.
>> + * @param min
>> + *   The value, in Hertz, to set the minimum frequency to.
>
> Is it really in Hertz? As far as I can tell, it's in steps of 100MHz 
> (BUS_FREQ).

Correct, the frequency changes in steps of 100MHz, but the value passed 
to 'min' is in kHz - will ammend the comments.