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

[Stephen Hemminger]

On Thu, 12 Sep 2024 10:38:11 +0800
Huisong Li <lihuisong at 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.

It also ends up in the section associated with Intel UnCore.
It would be better after the Turbo Boost section.



> +	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().

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));