Re: [dpdk-dev] [PATCH v6 05/10] power: add PMD power management API and callback

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> From: Liang Ma <liang.j.ma@intel.com>
> 
> Add a simple on/off switch that will enable saving power when no
> packets are arriving. It is based on counting the number of empty
> polls and, when the number reaches a certain threshold, entering an
> architecture-defined optimized power state that will either wait
> until a TSC timestamp expires, or when packets arrive.
> 
> This API mandates a core-to-single-queue mapping (that is, multiple
> queued per device are supported, but they have to be polled on different
> cores).
> 
> This design is using PMD RX callbacks.
> 
> 1. UMWAIT/UMONITOR:
> 
>    When a certain threshold of empty polls is reached, the core will go
>    into a power optimized sleep while waiting on an address of next RX
>    descriptor to be written to.
> 
> 2. Pause instruction
> 
>    Instead of move the core into deeper C state, this method uses the
>    pause instruction to avoid busy polling.
> 
> 3. Frequency scaling
>    Reuse existing DPDK power library to scale up/down core frequency
>    depending on traffic volume.
> 
> Signed-off-by: Liang Ma <liang.j.ma@intel.com>
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---
> 
> Notes:
>     v6:
>     - Added wakeup mechanism for UMWAIT
>     - Removed memory allocation (everything is now allocated statically)
>     - Fixed various typos and comments
>     - Check for invalid queue ID
>     - Moved release notes to this patch
> 
>     v5:
>     - Make error checking more robust
>       - Prevent initializing scaling if ACPI or PSTATE env wasn't set
>       - Prevent initializing UMWAIT path if PMD doesn't support get_wake_addr
>     - Add some debug logging
>     - Replace x86-specific code path to generic path using the intrinsic check
> 
>  doc/guides/rel_notes/release_20_11.rst |  11 +
>  lib/librte_power/meson.build           |   5 +-
>  lib/librte_power/rte_power_pmd_mgmt.c  | 300 +++++++++++++++++++++++++
>  lib/librte_power/rte_power_pmd_mgmt.h  |  92 ++++++++
>  lib/librte_power/rte_power_version.map |   4 +
>  5 files changed, 410 insertions(+), 2 deletions(-)
>  create mode 100644 lib/librte_power/rte_power_pmd_mgmt.c
>  create mode 100644 lib/librte_power/rte_power_pmd_mgmt.h
> 
> diff --git a/doc/guides/rel_notes/release_20_11.rst b/doc/guides/rel_notes/release_20_11.rst
> index ca4f43f7f9..06b822aa36 100644
> --- a/doc/guides/rel_notes/release_20_11.rst
> +++ b/doc/guides/rel_notes/release_20_11.rst
> @@ -197,6 +197,17 @@ New Features
>    * Added new ``RTE_ACL_CLASSIFY_AVX512X32`` vector implementation,
>      which can process up to 32 flows in parallel. Requires AVX512 support.
> 
> +* **Add PMD power management mechanism**
> +
> +  3 new Ethernet PMD power management mechanism is added through existing
> +  RX callback infrastructure.
> +
> +  * Add power saving scheme based on UMWAIT instruction (x86 only)
> +  * Add power saving scheme based on ``rte_pause()``
> +  * Add power saving scheme based on frequency scaling through the power library
> +  * Add new EXPERIMENTAL API ``rte_power_pmd_mgmt_queue_enable()``
> +  * Add new EXPERIMENTAL API ``rte_power_pmd_mgmt_queue_disable()``
> +
> 
>  Removed Items
>  -------------
> diff --git a/lib/librte_power/meson.build b/lib/librte_power/meson.build
> index 78c031c943..cc3c7a8646 100644
> --- a/lib/librte_power/meson.build
> +++ b/lib/librte_power/meson.build
> @@ -9,6 +9,7 @@ sources = files('rte_power.c', 'power_acpi_cpufreq.c',
>  		'power_kvm_vm.c', 'guest_channel.c',
>  		'rte_power_empty_poll.c',
>  		'power_pstate_cpufreq.c',
> +		'rte_power_pmd_mgmt.c',
>  		'power_common.c')
> -headers = files('rte_power.h','rte_power_empty_poll.h')
> -deps += ['timer']
> +headers = files('rte_power.h','rte_power_empty_poll.h','rte_power_pmd_mgmt.h')
> +deps += ['timer' ,'ethdev']
> diff --git a/lib/librte_power/rte_power_pmd_mgmt.c b/lib/librte_power/rte_power_pmd_mgmt.c
> new file mode 100644
> index 0000000000..2b7d2a1a46
> --- /dev/null
> +++ b/lib/librte_power/rte_power_pmd_mgmt.c
> @@ -0,0 +1,300 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2010-2020 Intel Corporation
> + */
> +
> +#include <rte_lcore.h>
> +#include <rte_cycles.h>
> +#include <rte_cpuflags.h>
> +#include <rte_malloc.h>
> +#include <rte_ethdev.h>
> +#include <rte_power_intrinsics.h>
> +
> +#include "rte_power_pmd_mgmt.h"
> +
> +#define EMPTYPOLL_MAX  512
> +
> +/**
> + * Possible power management states of an ethdev port.
> + */
> +enum pmd_mgmt_state {
> +	/** Device power management is disabled. */
> +	PMD_MGMT_DISABLED = 0,
> +	/** Device power management is enabled. */
> +	PMD_MGMT_ENABLED,
> +};
> +
> +struct pmd_queue_cfg {
> +	enum pmd_mgmt_state pwr_mgmt_state;
> +	/**< State of power management for this queue */
> +	enum rte_power_pmd_mgmt_type cb_mode;
> +	/**< Callback mode for this queue */
> +	const struct rte_eth_rxtx_callback *cur_cb;
> +	/**< Callback instance */
> +	rte_spinlock_t umwait_lock;
> +	/**< Per-queue status lock - used only for UMWAIT mode */
> +	volatile void *wait_addr;
> +	/**< UMWAIT wakeup address */
> +	uint64_t empty_poll_stats;
> +	/**< Number of empty polls */
> +} __rte_cache_aligned;
> +
> +static struct pmd_queue_cfg port_cfg[RTE_MAX_ETHPORTS][RTE_MAX_QUEUES_PER_PORT];
> +
> +/* trigger a write to the cache line we're waiting on */
> +static void umwait_wakeup(volatile void *addr)
> +{
> +	uint64_t val;
> +
> +	val = __atomic_load_n((volatile uint64_t *)addr, __ATOMIC_RELAXED);
> +	__atomic_compare_exchange_n((volatile uint64_t *)addr, &val, val, 0,
> +			__ATOMIC_RELAXED, __ATOMIC_RELAXED);
> +}
> +
> +static uint16_t
> +clb_umwait(uint16_t port_id, uint16_t qidx,
> +		struct rte_mbuf **pkts __rte_unused, uint16_t nb_rx,
> +		uint16_t max_pkts __rte_unused, void *addr __rte_unused)
> +{
> +
> +	struct pmd_queue_cfg *q_conf;
> +
> +	q_conf = &port_cfg[port_id][qidx];
> +
> +	if (unlikely(nb_rx == 0)) {
> +		q_conf->empty_poll_stats++;
> +		if (unlikely(q_conf->empty_poll_stats > EMPTYPOLL_MAX)) {
> +			volatile void *target_addr;
> +			uint64_t expected, mask;
> +			uint16_t ret;
> +			uint8_t data_sz;
> +
> +			/*
> +			 * get address of next descriptor in the RX
> +			 * ring for this queue, as well as expected
> +			 * value and a mask.
> +			 */
> +			ret = rte_eth_get_wake_addr(port_id, qidx,
> +					&target_addr, &expected, &mask,
> +					&data_sz);
> +			if (ret == 0) {
> +				/*
> +				 * we need to ensure we can wake up by another
> +				 * thread triggering a write, so we need the
> +				 * address to always be up to date.
> +				 */
> +				rte_spinlock_lock(&q_conf->umwait_lock);


I think you need to check state here, and _disable() have to set state with lock grabbed.
Otherwise this lock wouldn't protect you from race conditions.
As an example:

CP@T0:
	rte_spinlock_lock(&queue_cfg->umwait_lock);
	if (queue_cfg->wait_addr != NULL) //wait_addr == NULL, fallthrough
	rte_spinlock_unlock(&queue_cfg->umwait_lock);

DP@T1:
	rte_spinlock_lock(&queue_cfg->umwait_lock);
	queue_cfg->wait_addr = target_addr;
	monitor_sync(...);  // DP was put to sleep

CP@T2:
	queue_cfg->cur_cb = NULL;
	queue_cfg->pwr_mgmt_state = PMD_MGMT_DISABLED;
	ret = 0;

rte_power_pmd_mgmt_queue_disable() finished with success,
but DP core wasn't wokenup.

To be more specific:
clb_umwait(...) {
	...
	lock(&qcfg->lck);
	if (qcfg->state == ENABLED)  {
		qcfg->wake_addr = addr;
		monitor_sync(addr, ...,&qcfg->lck);
	}
	unlock(&qcfg->lck); 
	...
}

_disable(...) {
	...
	lock(&qcfg->lck);
	qcfg->state = DISABLED;
	if (qcfg->wake_addr != NULL)
		monitor_wakeup(qcfg->wake_addr);
	unlock(&qcfg->lock);
	...
}

> +				q_conf->wait_addr = target_addr;
> +				/* -1ULL is maximum value for TSC */
> +				rte_power_monitor_sync(target_addr, expected,
> +						mask, -1ULL, data_sz,
> +						&q_conf->umwait_lock);
> +				/* erase the address */
> +				q_conf->wait_addr = NULL;
> +				rte_spinlock_unlock(&q_conf->umwait_lock);
> +			}
> +		}
> +	} else
> +		q_conf->empty_poll_stats = 0;
> +
> +	return nb_rx;
> +}
> +
> +static uint16_t
> +clb_pause(uint16_t port_id, uint16_t qidx,
> +		struct rte_mbuf **pkts __rte_unused, uint16_t nb_rx,
> +		uint16_t max_pkts __rte_unused, void *addr __rte_unused)
> +{
> +	struct pmd_queue_cfg *q_conf;
> +
> +	q_conf = &port_cfg[port_id][qidx];
> +
> +	if (unlikely(nb_rx == 0)) {
> +		q_conf->empty_poll_stats++;
> +		/* sleep for 1 microsecond */
> +		if (unlikely(q_conf->empty_poll_stats > EMPTYPOLL_MAX))
> +			rte_delay_us(1);
> +	} else
> +		q_conf->empty_poll_stats = 0;
> +
> +	return nb_rx;
> +}
> +
> +static uint16_t
> +clb_scale_freq(uint16_t port_id, uint16_t qidx,
> +		struct rte_mbuf **pkts __rte_unused, uint16_t nb_rx,
> +		uint16_t max_pkts __rte_unused, void *_  __rte_unused)
> +{
> +	struct pmd_queue_cfg *q_conf;
> +
> +	q_conf = &port_cfg[port_id][qidx];
> +
> +	if (unlikely(nb_rx == 0)) {
> +		q_conf->empty_poll_stats++;
> +		if (unlikely(q_conf->empty_poll_stats > EMPTYPOLL_MAX))
> +			/* scale down freq */
> +			rte_power_freq_min(rte_lcore_id());
> +	} else {
> +		q_conf->empty_poll_stats = 0;
> +		/* scale up freq */
> +		rte_power_freq_max(rte_lcore_id());
> +	}
> +
> +	return nb_rx;
> +}
> +
> +int
> +rte_power_pmd_mgmt_queue_enable(unsigned int lcore_id,
> +		uint16_t port_id, uint16_t queue_id,
> +		enum rte_power_pmd_mgmt_type mode)
> +{
> +	struct rte_eth_dev *dev;
> +	struct pmd_queue_cfg *queue_cfg;
> +	int ret;
> +
> +	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -EINVAL);
> +	dev = &rte_eth_devices[port_id];
> +
> +	/* check if queue id is valid */
> +	if (queue_id >= dev->data->nb_rx_queues ||
> +			queue_id >= RTE_MAX_QUEUES_PER_PORT) {
> +		return -EINVAL;
> +	}
> +
> +	queue_cfg = &port_cfg[port_id][queue_id];
> +
> +	if (queue_cfg->pwr_mgmt_state == PMD_MGMT_ENABLED) {
> +		ret = -EINVAL;
> +		goto end;
> +	}
> +
> +	switch (mode) {
> +	case RTE_POWER_MGMT_TYPE_WAIT:
> +	{
> +		/* check if rte_power_monitor is supported */
> +		uint64_t dummy_expected, dummy_mask;
> +		struct rte_cpu_intrinsics i;
> +		volatile void *dummy_addr;
> +		uint8_t dummy_sz;
> +
> +		rte_cpu_get_intrinsics_support(&i);
> +
> +		if (!i.power_monitor) {
> +			RTE_LOG(DEBUG, POWER, "Monitoring intrinsics are not supported\n");
> +			ret = -ENOTSUP;
> +			goto end;
> +		}
> +
> +		/* check if the device supports the necessary PMD API */
> +		if (rte_eth_get_wake_addr(port_id, queue_id,
> +				&dummy_addr, &dummy_expected,
> +				&dummy_mask, &dummy_sz) == -ENOTSUP) {
> +			RTE_LOG(DEBUG, POWER, "The device does not support rte_eth_rxq_ring_addr_get\n");
> +			ret = -ENOTSUP;
> +			goto end;
> +		}
> +		/* initialize UMWAIT spinlock */
> +		rte_spinlock_init(&queue_cfg->umwait_lock);

I think don't need to do that.
It supposed to be in valid state (otherwise you are probably in trouble anyway).

> +
> +		/* initialize data before enabling the callback */
> +		queue_cfg->empty_poll_stats = 0;
> +		queue_cfg->cb_mode = mode;
> +		queue_cfg->pwr_mgmt_state = PMD_MGMT_ENABLED;
> +
> +		queue_cfg->cur_cb = rte_eth_add_rx_callback(port_id, queue_id,
> +				clb_umwait, NULL);

Would be a bit cleaner/nicer to move add_rx_callback out of switch() {}
As you have to do it always anyway.
Same thought for disable() and remove_rx_callback().

> +		break;
> +	}
> +	case RTE_POWER_MGMT_TYPE_SCALE:
> +	{
> +		enum power_management_env env;
> +		/* only PSTATE and ACPI modes are supported */
> +		if (!rte_power_check_env_supported(PM_ENV_ACPI_CPUFREQ) &&
> +				!rte_power_check_env_supported(
> +					PM_ENV_PSTATE_CPUFREQ)) {
> +			RTE_LOG(DEBUG, POWER, "Neither ACPI nor PSTATE modes are supported\n");
> +			ret = -ENOTSUP;
> +			goto end;
> +		}
> +		/* ensure we could initialize the power library */
> +		if (rte_power_init(lcore_id)) {
> +			ret = -EINVAL;
> +			goto end;
> +		}
> +		/* ensure we initialized the correct env */
> +		env = rte_power_get_env();
> +		if (env != PM_ENV_ACPI_CPUFREQ &&
> +				env != PM_ENV_PSTATE_CPUFREQ) {
> +			RTE_LOG(DEBUG, POWER, "Neither ACPI nor PSTATE modes were initialized\n");
> +			ret = -ENOTSUP;
> +			goto end;
> +		}
> +		/* initialize data before enabling the callback */
> +		queue_cfg->empty_poll_stats = 0;
> +		queue_cfg->cb_mode = mode;
> +		queue_cfg->pwr_mgmt_state = PMD_MGMT_ENABLED;
> +
> +		queue_cfg->cur_cb = rte_eth_add_rx_callback(port_id,
> +				queue_id, clb_scale_freq, NULL);
> +		break;
> +	}
> +	case RTE_POWER_MGMT_TYPE_PAUSE:
> +		/* initialize data before enabling the callback */
> +		queue_cfg->empty_poll_stats = 0;
> +		queue_cfg->cb_mode = mode;
> +		queue_cfg->pwr_mgmt_state = PMD_MGMT_ENABLED;
> +
> +		queue_cfg->cur_cb = rte_eth_add_rx_callback(port_id, queue_id,
> +				clb_pause, NULL);
> +		break;
> +	}
> +	ret = 0;
> +
> +end:
> +	return ret;
> +}
> +
> +int
> +rte_power_pmd_mgmt_queue_disable(unsigned int lcore_id,
> +		uint16_t port_id, uint16_t queue_id)
> +{
> +	struct pmd_queue_cfg *queue_cfg;
> +	int ret;
> +
> +	queue_cfg = &port_cfg[port_id][queue_id];
> +
> +	if (queue_cfg->pwr_mgmt_state == PMD_MGMT_DISABLED) {
> +		ret = -EINVAL;
> +		goto end;
> +	}
> +
> +	switch (queue_cfg->cb_mode) {
> +	case RTE_POWER_MGMT_TYPE_WAIT:
> +		rte_spinlock_lock(&queue_cfg->umwait_lock);
> +
> +		/* wake up the core from UMWAIT sleep, if any */
> +		if (queue_cfg->wait_addr != NULL)
> +			umwait_wakeup(queue_cfg->wait_addr);
> +
> +		rte_spinlock_unlock(&queue_cfg->umwait_lock);
> +		/* fall-through */
> +	case RTE_POWER_MGMT_TYPE_PAUSE:
> +		rte_eth_remove_rx_callback(port_id, queue_id,
> +				queue_cfg->cur_cb);
> +		break;
> +	case RTE_POWER_MGMT_TYPE_SCALE:
> +		rte_power_freq_max(lcore_id);
> +		rte_eth_remove_rx_callback(port_id, queue_id,
> +				queue_cfg->cur_cb);
> +		rte_power_exit(lcore_id);
> +		break;
> +	}
> +	/*
> +	 * we don't free the RX callback here because it is unsafe to do so
> +	 * unless we know for a fact that all data plane threads have stopped.
> +	 */
> +	queue_cfg->cur_cb = NULL;
> +	queue_cfg->pwr_mgmt_state = PMD_MGMT_DISABLED;
> +	ret = 0;
> +end:
> +	return ret;
> +}
> diff --git a/lib/librte_power/rte_power_pmd_mgmt.h b/lib/librte_power/rte_power_pmd_mgmt.h
> new file mode 100644
> index 0000000000..a7a3f98268
> --- /dev/null
> +++ b/lib/librte_power/rte_power_pmd_mgmt.h
> @@ -0,0 +1,92 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2010-2020 Intel Corporation
> + */
> +
> +#ifndef _RTE_POWER_PMD_MGMT_H
> +#define _RTE_POWER_PMD_MGMT_H
> +
> +/**
> + * @file
> + * RTE PMD Power Management
> + */
> +#include <stdint.h>
> +#include <stdbool.h>
> +
> +#include <rte_common.h>
> +#include <rte_byteorder.h>
> +#include <rte_log.h>
> +#include <rte_power.h>
> +#include <rte_atomic.h>
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +/**
> + * PMD Power Management Type
> + */
> +enum rte_power_pmd_mgmt_type {
> +	/** WAIT callback mode. */
> +	RTE_POWER_MGMT_TYPE_WAIT = 1,
> +	/** PAUSE callback mode. */
> +	RTE_POWER_MGMT_TYPE_PAUSE,
> +	/** Freq Scaling callback mode. */
> +	RTE_POWER_MGMT_TYPE_SCALE,
> +};
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
> + *
> + * Setup per-queue power management callback.
> + *
> + * @note This function is not thread-safe.
> + *
> + * @param lcore_id
> + *   lcore_id.
> + * @param port_id
> + *   The port identifier of the Ethernet device.
> + * @param queue_id
> + *   The queue identifier of the Ethernet device.
> + * @param mode
> + *   The power management callback function type.
> +
> + * @return
> + *   0 on success
> + *   <0 on error
> + */
> +__rte_experimental
> +int
> +rte_power_pmd_mgmt_queue_enable(unsigned int lcore_id,
> +				uint16_t port_id,
> +				uint16_t queue_id,
> +				enum rte_power_pmd_mgmt_type mode);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
> + *
> + * Remove per-queue power management callback.
> + *
> + * @note This function is not thread-safe.
> + *
> + * @param lcore_id
> + *   lcore_id.
> + * @param port_id
> + *   The port identifier of the Ethernet device.
> + * @param queue_id
> + *   The queue identifier of the Ethernet device.
> + * @return
> + *   0 on success
> + *   <0 on error
> + */
> +__rte_experimental
> +int
> +rte_power_pmd_mgmt_queue_disable(unsigned int lcore_id,
> +				uint16_t port_id,
> +				uint16_t queue_id);
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif
> diff --git a/lib/librte_power/rte_power_version.map b/lib/librte_power/rte_power_version.map
> index 69ca9af616..3f2f6cd6f6 100644
> --- a/lib/librte_power/rte_power_version.map
> +++ b/lib/librte_power/rte_power_version.map
> @@ -34,4 +34,8 @@ EXPERIMENTAL {
>  	rte_power_guest_channel_receive_msg;
>  	rte_power_poll_stat_fetch;
>  	rte_power_poll_stat_update;
> +	# added in 20.11
> +	rte_power_pmd_mgmt_queue_enable;
> +	rte_power_pmd_mgmt_queue_disable;
> +
>  };
> --
> 2.17.1