Re: [PATCH v9 1/2] power: introduce PM QoS API on CPU wide

[fengchengwen <fengchengwen@huawei.com>]

Hi Huisong

Please see comments inline.

Thanks

On 2024/8/9 17:50, Huisong Li wrote:
> 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 control this CPU's idle state
> selection and limit just enter the shallowest idle state to low the delay
> after sleep by setting strict resume latency (zero value).
> 
> Signed-off-by: Huisong Li <lihuisong@huawei.com>
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
> ---

...

> diff --git a/lib/power/rte_power_qos.c b/lib/power/rte_power_qos.c
> new file mode 100644
> index 0000000000..375746f832
> --- /dev/null
> +++ b/lib/power/rte_power_qos.c
> @@ -0,0 +1,114 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2024 HiSilicon Limited
> + */
> +
> +#include <errno.h>
> +#include <stdlib.h>
> +#include <string.h>
> +
> +#include <rte_lcore.h>
> +#include <rte_log.h>
> +
> +#include "power_common.h"
> +#include "rte_power_qos.h"
> +
> +#define PM_QOS_SYSFILE_RESUME_LATENCY_US	\
> +	"/sys/devices/system/cpu/cpu%u/power/pm_qos_resume_latency_us"
> +
> +int
> +rte_power_qos_set_cpu_resume_latency(uint16_t lcore_id, int latency)
> +{
> +	char buf[LINE_MAX];

no need LINE_MAX, [32] would enough.

> +	FILE *f;
> +	int ret;
> +
> +	if (!rte_lcore_is_enabled(lcore_id)) {
> +		POWER_LOG(ERR, "lcore id %u is not enabled", lcore_id);
> +		return -EINVAL;
> +	}
> +
> +	if (latency < 0) {
> +		POWER_LOG(ERR, "latency should be greater than and equal to 0");
> +		return -EINVAL;
> +	}
> +
> +	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;
> +	}
> +
> +	/*
> +	 * Based on the sysfs interface pm_qos_resume_latency_us under
> +	 * @PM_QOS_SYSFILE_RESUME_LATENCY_US directory in kernel, their meanning

meanning -> meaning

> +	 * is as follows for different input string.
> +	 * 1> the resume latency is 0 if the input is "n/a".
> +	 * 2> the resume latency is no constraint if the input is "0".
> +	 * 3> the resume latency is the actual value to be set.
> +	 */
> +	if (latency == 0)
> +		snprintf(buf, sizeof(buf), "%s", "n/a");
> +	else if (latency == RTE_POWER_QOS_RESUME_LATENCY_NO_CONSTRAINT)
> +		snprintf(buf, sizeof(buf), "%u", 0);
> +	else
> +		snprintf(buf, sizeof(buf), "%u", latency);
> +
> +	ret = write_core_sysfs_s(f, buf);
> +	if (ret != 0) {
> +		POWER_LOG(ERR, "Failed to write "PM_QOS_SYSFILE_RESUME_LATENCY_US, lcore_id);
> +		goto out;

no need of goto

> +	}
> +
> +out:
> +	if (f != NULL)
> +		fclose(f);

just fclose(f) because f is valid here.

> +
> +	return ret;
> +}
> +
> +int
> +rte_power_qos_get_cpu_resume_latency(uint16_t lcore_id)
> +{
> +	char buf[LINE_MAX];
> +	int latency = -1;
> +	FILE *f;
> +	int ret;
> +
> +	if (!rte_lcore_is_enabled(lcore_id)) {
> +		POWER_LOG(ERR, "lcore id %u is not enabled", lcore_id);
> +		return -EINVAL;
> +	}
> +
> +	ret = open_core_sysfs_file(&f, "r", 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;
> +	}
> +
> +	ret = read_core_sysfs_s(f, buf, sizeof(buf));
> +	if (ret != 0) {
> +		POWER_LOG(ERR, "Failed to read "PM_QOS_SYSFILE_RESUME_LATENCY_US, lcore_id);
> +		goto out;
> +	}
> +
> +	/*
> +	 * Based on the sysfs interface pm_qos_resume_latency_us under
> +	 * @PM_QOS_SYSFILE_RESUME_LATENCY_US directory in kernel, their meanning

meanning -> meaning

> +	 * is as follows for different output string.
> +	 * 1> the resume latency is 0 if the output is "n/a".
> +	 * 2> the resume latency is no constraint if the output is "0".
> +	 * 3> the resume latency is the actual value in used for other string.
> +	 */
> +	if (strcmp(buf, "n/a") == 0)
> +		latency = 0;
> +	else {
> +		latency = strtoul(buf, NULL, 10);
> +		latency = latency == 0 ? RTE_POWER_QOS_RESUME_LATENCY_NO_CONSTRAINT : latency;
> +	}
> +
> +out:
> +	if (f != NULL)
> +		fclose(f);

just fclose(f) because f is valid here.

> +
> +	return latency != -1 ? latency : ret;
> +}
> diff --git a/lib/power/rte_power_qos.h b/lib/power/rte_power_qos.h
> new file mode 100644
> index 0000000000..990c488373
> --- /dev/null
> +++ b/lib/power/rte_power_qos.h
> @@ -0,0 +1,73 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2024 HiSilicon Limited
> + */
> +
> +#ifndef RTE_POWER_QOS_H
> +#define RTE_POWER_QOS_H
> +
> +#include <stdint.h>
> +
> +#include <rte_compat.h>
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +/**
> + * @file rte_power_qos.h
> + *
> + * PM QoS API.
> + *
> + * The CPU-wide resume latency limit has a positive impact on this CPU's idle
> + * state selection in each cpuidle governor.
> + * Please see the PM QoS on CPU wide in the following link:
> + * https://www.kernel.org/doc/html/latest/admin-guide/abi-testing.html?highlight=pm_qos_resume_latency_us#abi-sys-devices-power-pm-qos-resume-latency-us
> + *
> + * 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.
> + *
> + * In these case, per-CPU PM QoS API can be used to control this CPU's idle
> + * state selection and limit just enter the shallowest idle state to low the
> + * delay after sleep by setting strict resume latency (zero value).
> + */
> +
> +#define RTE_POWER_QOS_STRICT_LATENCY_VALUE             0
> +#define RTE_POWER_QOS_RESUME_LATENCY_NO_CONSTRAINT    ((int)(UINT32_MAX >> 1))
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * @param lcore_id
> + *   target logical core id
> + *
> + * @param latency
> + *   The latency should be greater than and equal to zero in microseconds unit.
> + *
> + * @return
> + *   0 on success. Otherwise negative value is returned.
> + */
> +__rte_experimental
> +int rte_power_qos_set_cpu_resume_latency(uint16_t lcore_id, int latency);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Get the current resume latency of this logical core.
> + * The default value in kernel is @see RTE_POWER_QOS_RESUME_LATENCY_NO_CONSTRAINT
> + * if don't set it.
> + *
> + * @return
> + *   Negative value on failure.
> + *   >= 0 means the actual resume latency limit on this core.
> + */
> +__rte_experimental
> +int rte_power_qos_get_cpu_resume_latency(uint16_t lcore_id);
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* RTE_POWER_QOS_H */
> diff --git a/lib/power/version.map b/lib/power/version.map
> index c9a226614e..4e4955a4cf 100644
> --- a/lib/power/version.map
> +++ b/lib/power/version.map
> @@ -51,4 +51,8 @@ EXPERIMENTAL {
>  	rte_power_set_uncore_env;
>  	rte_power_uncore_freqs;
>  	rte_power_unset_uncore_env;
> +
> +	# added in 24.11
> +	rte_power_qos_set_cpu_resume_latency;
> +	rte_power_qos_get_cpu_resume_latency;

order by alphabetic.

another question, I think rename cpu with core maybe more accurate, despite sysfs export with cpu, but in DPDK it means core.
and there are some rte_power_core_xxx name in rte_power library, I think better to keep the same.

>  };
>