Re: [PATCH v10 1/2] power: introduce PM QoS API on CPU wide

["lihuisong (C)" <lihuisong@huawei.com>]

Hi Stephen,


在 2024/10/13 9:10, Stephen Hemminger 写道:
> On Thu, 12 Sep 2024 10:38:11 +0800
> Huisong Li <lihuisong@huawei.com> wrote:
>
>> +
>> +PM QoS
>> +------
>> +
>> +The deeper the idle state, the lower the power consumption, but the longer
>> +the resume time. Some service are delay sensitive and very except the low
>> +resume time, like interrupt packet receiving mode.
>> +
>> +And the "/sys/devices/system/cpu/cpuX/power/pm_qos_resume_latency_us" sysfs
>> +interface is used to set and get the resume latency limit on the cpuX for
>> +userspace. Each cpuidle governor in Linux select which idle state to enter
>> +based on this CPU resume latency in their idle task.
>> +
>> +The per-CPU PM QoS API can be used to set and get the CPU resume latency based
>> +on this sysfs.
>> +
>> +The ``rte_power_qos_set_cpu_resume_latency()`` function can control the CPU's
>> +idle state selection in Linux and limit just to enter the shallowest idle state
>> +to low the delay of resuming service after sleeping by setting strict resume
>> +latency (zero value).
>> +
>> +The ``rte_power_qos_get_cpu_resume_latency()`` function can get the resume
>> +latency on specified CPU.
>> +
> These paragraphs need some editing help. The wording is awkward,
> it uses passive voice, and does not seemed directed at a user audience.
> If you need help, a writer or AI might help clarify.
How about the following description:
-->
The "/sys/devices/system/cpu/cpuX/power/pm_qos_resume_latency_us" sysfs
interface is used to set and get the resume latency limit on the cpuX for
userspace. Each cpuidle governor in Linux select which idle state to enter
based on this CPU resume latency in their idle task.

The deeper the idle state, the lower the power consumption, but the longer
the resume time. Some service are delay sensitive and very except the low
resume time, like interrupt packet receiving mode.

The ``rte_power_qos_set_cpu_resume_latency()`` and 
``rte_power_qos_get_cpu_resume_latency()``
can set and get the CPU resume latency based on this per-CPU sysfs.

The ``rte_power_qos_set_cpu_resume_latency()`` can control the CPU's
idle state selection and limit to enter the shallowest idle state
to low the delay of resuming service by setting strict resume
latency (zero value) so as to get better performance.
>
> It also ends up in the section associated with Intel UnCore.
> It would be better after the Turbo Boost section.
Ack
>
>
>
>> +	ret = open_core_sysfs_file(&f, "w", PM_QOS_SYSFILE_RESUME_LATENCY_US, lcore_id);
>> +	if (ret != 0) {
>> +		POWER_LOG(ERR, "Failed to open "PM_QOS_SYSFILE_RESUME_LATENCY_US, lcore_id);
>> +		return ret;
>> +	}
> The function open_core_sysfs_file() should have been written to return FILE *
> and then it could have same attributes as fopen().
Do you mean we should save this handle for directly using it to get or 
set this resume latency?
If it is I understand, we cannot do it like this. Because qos driver in 
Linux use the "noop_llseek()" as the .llseek API.
>
> The message should include the error reason.
>
> 	if (open_core_sysfs_file(&f, "w", PM_QOS_SYSFILE_RESUME_LATENCY_US, lcore_id)) {
> 		POWER_LOG(ERR, "Failed to open " PM_QOS_SYSFILE_RESUME_LATENCY_US ": %s",
> 			lcore_id, strerror(errno));
Good idea.  Thanks.

>
> .