[v6,02/10] eal: add power management intrinsics

  From: Liang Ma <liang.j.ma@intel.com>

Add two new power management intrinsics, and provide an implementation
in eal/x86 based on UMONITOR/UMWAIT instructions. The instructions
are implemented as raw byte opcodes because there is not yet widespread
compiler support for these instructions.

The power management instructions provide an architecture-specific
function to either wait until a specified TSC timestamp is reached, or
optionally wait until either a TSC timestamp is reached or a memory
location is written to. The monitor function also provides an optional
comparison, to avoid sleeping when the expected write has already
happened, and no more writes are expected.

For more details, please refer to Intel(R) 64 and IA-32 Architectures
Software Developer's Manual, Volume 2.

Signed-off-by: Liang Ma <liang.j.ma@intel.com>
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: David Christensen <drc@linux.vnet.ibm.com>
---

Notes:
    v6:
    - Add spinlock-enabled version to allow pthread-wait-like
      constructs with umwait
    - Clarify comments
    - Added experimental tags to intrinsics
    - Added endianness support
    v5:
    - Removed return values
    - Simplified intrinsics and hardcoded C0.2 state
    - Added other arch stubs

 lib/librte_eal/arm/include/meson.build        |   1 +
 .../arm/include/rte_power_intrinsics.h        |  58 ++++++++
 .../include/generic/rte_power_intrinsics.h    | 111 +++++++++++++++
 lib/librte_eal/include/meson.build            |   1 +
 lib/librte_eal/ppc/include/meson.build        |   1 +
 .../ppc/include/rte_power_intrinsics.h        |  58 ++++++++
 lib/librte_eal/x86/include/meson.build        |   1 +
 .../x86/include/rte_power_intrinsics.h        | 132 ++++++++++++++++++
 8 files changed, 363 insertions(+)
 create mode 100644 lib/librte_eal/arm/include/rte_power_intrinsics.h
 create mode 100644 lib/librte_eal/include/generic/rte_power_intrinsics.h
 create mode 100644 lib/librte_eal/ppc/include/rte_power_intrinsics.h
 create mode 100644 lib/librte_eal/x86/include/rte_power_intrinsics.h
  

> 
> From: Liang Ma <liang.j.ma@intel.com>
> 
> Add two new power management intrinsics, and provide an implementation
> in eal/x86 based on UMONITOR/UMWAIT instructions. The instructions
> are implemented as raw byte opcodes because there is not yet widespread
> compiler support for these instructions.
> 
> The power management instructions provide an architecture-specific
> function to either wait until a specified TSC timestamp is reached, or
> optionally wait until either a TSC timestamp is reached or a memory
> location is written to. The monitor function also provides an optional
> comparison, to avoid sleeping when the expected write has already
> happened, and no more writes are expected.
> 
> For more details, please refer to Intel(R) 64 and IA-32 Architectures
> Software Developer's Manual, Volume 2.
> 
> Signed-off-by: Liang Ma <liang.j.ma@intel.com>
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> Acked-by: David Christensen <drc@linux.vnet.ibm.com>
> ---
> 
> Notes:
>     v6:
>     - Add spinlock-enabled version to allow pthread-wait-like
>       constructs with umwait
>     - Clarify comments
>     - Added experimental tags to intrinsics
>     - Added endianness support
>     v5:
>     - Removed return values
>     - Simplified intrinsics and hardcoded C0.2 state
>     - Added other arch stubs
> 
>  lib/librte_eal/arm/include/meson.build        |   1 +
>  .../arm/include/rte_power_intrinsics.h        |  58 ++++++++
>  .../include/generic/rte_power_intrinsics.h    | 111 +++++++++++++++
>  lib/librte_eal/include/meson.build            |   1 +
>  lib/librte_eal/ppc/include/meson.build        |   1 +
>  .../ppc/include/rte_power_intrinsics.h        |  58 ++++++++
>  lib/librte_eal/x86/include/meson.build        |   1 +
>  .../x86/include/rte_power_intrinsics.h        | 132 ++++++++++++++++++
>  8 files changed, 363 insertions(+)
>  create mode 100644 lib/librte_eal/arm/include/rte_power_intrinsics.h
>  create mode 100644 lib/librte_eal/include/generic/rte_power_intrinsics.h
>  create mode 100644 lib/librte_eal/ppc/include/rte_power_intrinsics.h
>  create mode 100644 lib/librte_eal/x86/include/rte_power_intrinsics.h
> 
> diff --git a/lib/librte_eal/arm/include/meson.build b/lib/librte_eal/arm/include/meson.build
> index 73b750a18f..c6a9f70d73 100644
> --- a/lib/librte_eal/arm/include/meson.build
> +++ b/lib/librte_eal/arm/include/meson.build
> @@ -20,6 +20,7 @@ arch_headers = files(
>  	'rte_pause_32.h',
>  	'rte_pause_64.h',
>  	'rte_pause.h',
> +	'rte_power_intrinsics.h',
>  	'rte_prefetch_32.h',
>  	'rte_prefetch_64.h',
>  	'rte_prefetch.h',
> diff --git a/lib/librte_eal/arm/include/rte_power_intrinsics.h b/lib/librte_eal/arm/include/rte_power_intrinsics.h
> new file mode 100644
> index 0000000000..b04ba10c76
> --- /dev/null
> +++ b/lib/librte_eal/arm/include/rte_power_intrinsics.h
> @@ -0,0 +1,58 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2020 Intel Corporation
> + */
> +
> +#ifndef _RTE_POWER_INTRINSIC_ARM_H_
> +#define _RTE_POWER_INTRINSIC_ARM_H_
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +#include <rte_common.h>
> +
> +#include "generic/rte_power_intrinsics.h"
> +
> +/**
> + * This function is not supported on ARM.
> + */

Here and in other places - please follow dpdk coding convention
for function definitions, i.e:
static inline void
rte_power_monitor(... 

> +static inline void rte_power_monitor(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz)
> +{
> +	RTE_SET_USED(p);
> +	RTE_SET_USED(expected_value);
> +	RTE_SET_USED(value_mask);
> +	RTE_SET_USED(tsc_timestamp);
> +	RTE_SET_USED(data_sz);
> +}

You can probably put NOP implementations of these rte_powe_* functions
into generic/rte_power_intrinsics.h.
So, wouldn't need to duplicate them for every non-supported arch.
Same as it was done for rte_wait_until_equal_*().

> +
> +/**
> + * This function is not supported on ARM.
> + */
> +static inline void rte_power_monitor_sync(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz,
> +		rte_spinlock_t *lck)
> +{
> +	RTE_SET_USED(p);
> +	RTE_SET_USED(expected_value);
> +	RTE_SET_USED(value_mask);
> +	RTE_SET_USED(tsc_timestamp);
> +	RTE_SET_USED(lck);
> +	RTE_SET_USED(data_sz);
> +}
> +
> +/**
> + * This function is not supported on ARM.
> + */
> +static inline void rte_power_pause(const uint64_t tsc_timestamp)
> +{
> +	RTE_SET_USED(tsc_timestamp);
> +}
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_POWER_INTRINSIC_ARM_H_ */
> diff --git a/lib/librte_eal/include/generic/rte_power_intrinsics.h b/lib/librte_eal/include/generic/rte_power_intrinsics.h
> new file mode 100644
> index 0000000000..f9522f2776
> --- /dev/null
> +++ b/lib/librte_eal/include/generic/rte_power_intrinsics.h
> @@ -0,0 +1,111 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2020 Intel Corporation
> + */
> +
> +#ifndef _RTE_POWER_INTRINSIC_H_
> +#define _RTE_POWER_INTRINSIC_H_
> +
> +#include <inttypes.h>
> +
> +#include <rte_compat.h>
> +#include <rte_spinlock.h>
> +
> +/**
> + * @file
> + * Advanced power management operations.
> + *
> + * This file define APIs for advanced power management,
> + * which are architecture-dependent.
> + */
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Monitor specific address for changes. This will cause the CPU to enter an
> + * architecture-defined optimized power state until either the specified
> + * memory address is written to, a certain TSC timestamp is reached, or other
> + * reasons cause the CPU to wake up.
> + *
> + * Additionally, an `expected` 64-bit value and 64-bit mask are provided. If
> + * mask is non-zero, the current value pointed to by the `p` pointer will be
> + * checked against the expected value, and if they match, the entering of
> + * optimized power state may be aborted.
> + *
> + * @param p
> + *   Address to monitor for changes. Must be aligned on an 64-byte boundary.

Is 64B alignment really needed?


> + * @param expected_value
> + *   Before attempting the monitoring, the `p` address may be read and compared
> + *   against this value. If `value_mask` is zero, this step will be skipped.
> + * @param value_mask
> + *   The 64-bit mask to use to extract current value from `p`.
> + * @param tsc_timestamp
> + *   Maximum TSC timestamp to wait for. Note that the wait behavior is
> + *   architecture-dependent.
> + * @param data_sz
> + *   Data size (in bytes) that will be used to compare expected value with the
> + *   memory address. Can be 1, 2, 4 or 8. Supplying any other value will lead
> + *   to undefined result.
> + */
> +__rte_experimental
> +static inline void rte_power_monitor(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Monitor specific address for changes. This will cause the CPU to enter an
> + * architecture-defined optimized power state until either the specified
> + * memory address is written to, a certain TSC timestamp is reached, or other
> + * reasons cause the CPU to wake up.
> + *
> + * Additionally, an `expected` 64-bit value and 64-bit mask are provided. If
> + * mask is non-zero, the current value pointed to by the `p` pointer will be
> + * checked against the expected value, and if they match, the entering of
> + * optimized power state may be aborted.
> + *
> + * This call will also lock a spinlock on entering sleep, and release it on
> + * waking up the CPU.
> + *
> + * @param p
> + *   Address to monitor for changes. Must be aligned on an 64-byte boundary.
> + * @param expected_value
> + *   Before attempting the monitoring, the `p` address may be read and compared
> + *   against this value. If `value_mask` is zero, this step will be skipped.
> + * @param value_mask
> + *   The 64-bit mask to use to extract current value from `p`.
> + * @param tsc_timestamp
> + *   Maximum TSC timestamp to wait for. Note that the wait behavior is
> + *   architecture-dependent.
> + * @param data_sz
> + *   Data size (in bytes) that will be used to compare expected value with the
> + *   memory address. Can be 1, 2, 4 or 8. Supplying any other value will lead
> + *   to undefined result.
> + * @param lck
> + *   A spinlock that must be locked before entering the function, will be
> + *   unlocked while the CPU is sleeping, and will be locked again once the CPU
> + *   wakes up.
> + */
> +__rte_experimental
> +static inline void rte_power_monitor_sync(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz,
> +		rte_spinlock_t *lck);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Enter an architecture-defined optimized power state until a certain TSC
> + * timestamp is reached.
> + *
> + * @param tsc_timestamp
> + *   Maximum TSC timestamp to wait for. Note that the wait behavior is
> + *   architecture-dependent.
> + */
> +__rte_experimental
> +static inline void rte_power_pause(const uint64_t tsc_timestamp);
> +
> +#endif /* _RTE_POWER_INTRINSIC_H_ */
> diff --git a/lib/librte_eal/include/meson.build b/lib/librte_eal/include/meson.build
> index cd09027958..3a12e87e19 100644
> --- a/lib/librte_eal/include/meson.build
> +++ b/lib/librte_eal/include/meson.build
> @@ -60,6 +60,7 @@ generic_headers = files(
>  	'generic/rte_memcpy.h',
>  	'generic/rte_pause.h',
>  	'generic/rte_prefetch.h',
> +	'generic/rte_power_intrinsics.h',
>  	'generic/rte_rwlock.h',
>  	'generic/rte_spinlock.h',
>  	'generic/rte_ticketlock.h',
> diff --git a/lib/librte_eal/ppc/include/meson.build b/lib/librte_eal/ppc/include/meson.build
> index ab4bd28092..0873b2aecb 100644
> --- a/lib/librte_eal/ppc/include/meson.build
> +++ b/lib/librte_eal/ppc/include/meson.build
> @@ -10,6 +10,7 @@ arch_headers = files(
>  	'rte_io.h',
>  	'rte_memcpy.h',
>  	'rte_pause.h',
> +	'rte_power_intrinsics.h',
>  	'rte_prefetch.h',
>  	'rte_rwlock.h',
>  	'rte_spinlock.h',
> diff --git a/lib/librte_eal/ppc/include/rte_power_intrinsics.h b/lib/librte_eal/ppc/include/rte_power_intrinsics.h
> new file mode 100644
> index 0000000000..3bceefdc3f
> --- /dev/null
> +++ b/lib/librte_eal/ppc/include/rte_power_intrinsics.h
> @@ -0,0 +1,58 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2020 Intel Corporation
> + */
> +
> +#ifndef _RTE_POWER_INTRINSIC_PPC_H_
> +#define _RTE_POWER_INTRINSIC_PPC_H_
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +#include <rte_common.h>
> +
> +#include "generic/rte_power_intrinsics.h"
> +
> +/**
> + * This function is not supported on PPC64.
> + */
> +static inline void rte_power_monitor(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz)
> +{
> +	RTE_SET_USED(p);
> +	RTE_SET_USED(expected_value);
> +	RTE_SET_USED(value_mask);
> +	RTE_SET_USED(tsc_timestamp);
> +	RTE_SET_USED(data_sz);
> +}
> +
> +/**
> + * This function is not supported on PPC64.
> + */
> +static inline void rte_power_monitor_sync(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz,
> +		rte_spinlock_t *lck)
> +{
> +	RTE_SET_USED(p);
> +	RTE_SET_USED(expected_value);
> +	RTE_SET_USED(value_mask);
> +	RTE_SET_USED(tsc_timestamp);
> +	RTE_SET_USED(lck);
> +	RTE_SET_USED(data_sz);
> +}
> +
> +/**
> + * This function is not supported on PPC64.
> + */
> +static inline void rte_power_pause(const uint64_t tsc_timestamp)
> +{
> +	RTE_SET_USED(tsc_timestamp);
> +}
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_POWER_INTRINSIC_PPC_H_ */
> diff --git a/lib/librte_eal/x86/include/meson.build b/lib/librte_eal/x86/include/meson.build
> index f0e998c2fe..494a8142a2 100644
> --- a/lib/librte_eal/x86/include/meson.build
> +++ b/lib/librte_eal/x86/include/meson.build
> @@ -13,6 +13,7 @@ arch_headers = files(
>  	'rte_io.h',
>  	'rte_memcpy.h',
>  	'rte_prefetch.h',
> +	'rte_power_intrinsics.h',
>  	'rte_pause.h',
>  	'rte_rtm.h',
>  	'rte_rwlock.h',
> diff --git a/lib/librte_eal/x86/include/rte_power_intrinsics.h b/lib/librte_eal/x86/include/rte_power_intrinsics.h
> new file mode 100644
> index 0000000000..9ac8e6eef6
> --- /dev/null
> +++ b/lib/librte_eal/x86/include/rte_power_intrinsics.h
> @@ -0,0 +1,132 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2020 Intel Corporation
> + */
> +
> +#ifndef _RTE_POWER_INTRINSIC_X86_64_H_
> +#define _RTE_POWER_INTRINSIC_X86_64_H_

Why '_64_H'?
My understanding was these ops are supported 32-bit mode too. 

> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +#include <rte_common.h>
> +
> +#include "generic/rte_power_intrinsics.h"
> +
> +static inline uint64_t __get_umwait_val(const volatile void *p,
> +		const uint8_t sz)
> +{
> +	switch (sz) {
> +	case 1:

Just as a nit:
case sizeof(type_x):
	return *(const volatile type_x *)p;

> +		return *(const volatile uint8_t *)p;
> +	case 2:
> +		return *(const volatile uint16_t *)p;
> +	case 4:
> +		return *(const volatile uint32_t *)p;
> +	case 8:
> +		return *(const volatile uint64_t *)p;
> +	default:
> +		/* this is an intrinsic, so we can't have any error handling */

RTE_ASSERT(0); ?

> +		return 0;
> +	}
> +}
> +
> +/**
> + * This function uses UMONITOR/UMWAIT instructions and will enter C0.2 state.
> + * For more information about usage of these instructions, please refer to
> + * Intel(R) 64 and IA-32 Architectures Software Developer's Manual.
> + */
> +static inline void rte_power_monitor(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz)
> +{
> +	const uint32_t tsc_l = (uint32_t)tsc_timestamp;
> +	const uint32_t tsc_h = (uint32_t)(tsc_timestamp >> 32);
> +	/*
> +	 * we're using raw byte codes for now as only the newest compiler
> +	 * versions support this instruction natively.
> +	 */
> +
> +	/* set address for UMONITOR */
> +	asm volatile(".byte 0xf3, 0x0f, 0xae, 0xf7;"
> +			:
> +			: "D"(p));
> +
> +	if (value_mask) {
> +		const uint64_t cur_value = __get_umwait_val(p, data_sz);
> +		const uint64_t masked = cur_value & value_mask;
> +
> +		/* if the masked value is already matching, abort */
> +		if (masked == expected_value)
> +			return;
> +	}
> +	/* execute UMWAIT */
> +	asm volatile(".byte 0xf2, 0x0f, 0xae, 0xf7;"
> +			: /* ignore rflags */
> +			: "D"(0), /* enter C0.2 */
> +			  "a"(tsc_l), "d"(tsc_h));
> +}
> +
> +/**
> + * This function uses UMONITOR/UMWAIT instructions and will enter C0.2 state.
> + * For more information about usage of these instructions, please refer to
> + * Intel(R) 64 and IA-32 Architectures Software Developer's Manual.
> + */
> +static inline void rte_power_monitor_sync(const volatile void *p,
> +		const uint64_t expected_value, const uint64_t value_mask,
> +		const uint64_t tsc_timestamp, const uint8_t data_sz,
> +		rte_spinlock_t *lck)
> +{
> +	const uint32_t tsc_l = (uint32_t)tsc_timestamp;
> +	const uint32_t tsc_h = (uint32_t)(tsc_timestamp >> 32);
> +	/*
> +	 * we're using raw byte codes for now as only the newest compiler
> +	 * versions support this instruction natively.
> +	 */
> +
> +	/* set address for UMONITOR */
> +	asm volatile(".byte 0xf3, 0x0f, 0xae, 0xf7;"
> +			:
> +			: "D"(p));
> +
> +	if (value_mask) {
> +		const uint64_t cur_value = __get_umwait_val(p, data_sz);
> +		const uint64_t masked = cur_value & value_mask;
> +
> +		/* if the masked value is already matching, abort */
> +		if (masked == expected_value)
> +			return;
> +	}
> +	rte_spinlock_unlock(lck);
> +
> +	/* execute UMWAIT */
> +	asm volatile(".byte 0xf2, 0x0f, 0xae, 0xf7;"
> +			: /* ignore rflags */
> +			: "D"(0), /* enter C0.2 */
> +			  "a"(tsc_l), "d"(tsc_h));
> +
> +	rte_spinlock_lock(lck);
> +}
> +
> +/**
> + * This function uses TPAUSE instruction  and will enter C0.2 state. For more
> + * information about usage of this instruction, please refer to Intel(R) 64 and
> + * IA-32 Architectures Software Developer's Manual.
> + */
> +static inline void rte_power_pause(const uint64_t tsc_timestamp)
> +{
> +	const uint32_t tsc_l = (uint32_t)tsc_timestamp;
> +	const uint32_t tsc_h = (uint32_t)(tsc_timestamp >> 32);
> +
> +	/* execute TPAUSE */
> +	asm volatile(".byte 0x66, 0x0f, 0xae, 0xf7;"
> +		: /* ignore rflags */
> +		: "D"(0), /* enter C0.2 */
> +		  "a"(tsc_l), "d"(tsc_h));
> +}
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_POWER_INTRINSIC_X86_64_H_ */
> --
> 2.17.1
  

On 14-Oct-20 6:48 PM, Ananyev, Konstantin wrote:
> 
> 
>>
>> From: Liang Ma <liang.j.ma@intel.com>
>>
>> Add two new power management intrinsics, and provide an implementation
>> in eal/x86 based on UMONITOR/UMWAIT instructions. The instructions
>> are implemented as raw byte opcodes because there is not yet widespread
>> compiler support for these instructions.
>>
>> The power management instructions provide an architecture-specific
>> function to either wait until a specified TSC timestamp is reached, or
>> optionally wait until either a TSC timestamp is reached or a memory
>> location is written to. The monitor function also provides an optional
>> comparison, to avoid sleeping when the expected write has already
>> happened, and no more writes are expected.
>>
>> For more details, please refer to Intel(R) 64 and IA-32 Architectures
>> Software Developer's Manual, Volume 2.
>>
>> Signed-off-by: Liang Ma <liang.j.ma@intel.com>
>> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
>> Acked-by: David Christensen <drc@linux.vnet.ibm.com>
>> ---
>>
>> Notes:
>>      v6:
>>      - Add spinlock-enabled version to allow pthread-wait-like
>>        constructs with umwait
>>      - Clarify comments
>>      - Added experimental tags to intrinsics
>>      - Added endianness support
>>      v5:
>>      - Removed return values
>>      - Simplified intrinsics and hardcoded C0.2 state
>>      - Added other arch stubs
>>
>>   lib/librte_eal/arm/include/meson.build        |   1 +
>>   .../arm/include/rte_power_intrinsics.h        |  58 ++++++++
>>   .../include/generic/rte_power_intrinsics.h    | 111 +++++++++++++++
>>   lib/librte_eal/include/meson.build            |   1 +
>>   lib/librte_eal/ppc/include/meson.build        |   1 +
>>   .../ppc/include/rte_power_intrinsics.h        |  58 ++++++++
>>   lib/librte_eal/x86/include/meson.build        |   1 +
>>   .../x86/include/rte_power_intrinsics.h        | 132 ++++++++++++++++++
>>   8 files changed, 363 insertions(+)
>>   create mode 100644 lib/librte_eal/arm/include/rte_power_intrinsics.h
>>   create mode 100644 lib/librte_eal/include/generic/rte_power_intrinsics.h
>>   create mode 100644 lib/librte_eal/ppc/include/rte_power_intrinsics.h
>>   create mode 100644 lib/librte_eal/x86/include/rte_power_intrinsics.h
>>
>> diff --git a/lib/librte_eal/arm/include/meson.build b/lib/librte_eal/arm/include/meson.build
>> index 73b750a18f..c6a9f70d73 100644
>> --- a/lib/librte_eal/arm/include/meson.build
>> +++ b/lib/librte_eal/arm/include/meson.build
>> @@ -20,6 +20,7 @@ arch_headers = files(
>>   'rte_pause_32.h',
>>   'rte_pause_64.h',
>>   'rte_pause.h',
>> +'rte_power_intrinsics.h',
>>   'rte_prefetch_32.h',
>>   'rte_prefetch_64.h',
>>   'rte_prefetch.h',
>> diff --git a/lib/librte_eal/arm/include/rte_power_intrinsics.h b/lib/librte_eal/arm/include/rte_power_intrinsics.h
>> new file mode 100644
>> index 0000000000..b04ba10c76
>> --- /dev/null
>> +++ b/lib/librte_eal/arm/include/rte_power_intrinsics.h
>> @@ -0,0 +1,58 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(c) 2020 Intel Corporation
>> + */
>> +
>> +#ifndef _RTE_POWER_INTRINSIC_ARM_H_
>> +#define _RTE_POWER_INTRINSIC_ARM_H_
>> +
>> +#ifdef __cplusplus
>> +extern "C" {
>> +#endif
>> +
>> +#include <rte_common.h>
>> +
>> +#include "generic/rte_power_intrinsics.h"
>> +
>> +/**
>> + * This function is not supported on ARM.
>> + */
> 
> Here and in other places - please follow dpdk coding convention
> for function definitions, i.e:
> static inline void
> rte_power_monitor(...
> 

Yep, will do.

>> +static inline void rte_power_monitor(const volatile void *p,
>> +const uint64_t expected_value, const uint64_t value_mask,
>> +const uint64_t tsc_timestamp, const uint8_t data_sz)
>> +{
>> +RTE_SET_USED(p);
>> +RTE_SET_USED(expected_value);
>> +RTE_SET_USED(value_mask);
>> +RTE_SET_USED(tsc_timestamp);
>> +RTE_SET_USED(data_sz);
>> +}
> 
> You can probably put NOP implementations of these rte_powe_* functions
> into generic/rte_power_intrinsics.h.
> So, wouldn't need to duplicate them for every non-supported arch.
> Same as it was done for rte_wait_until_equal_*().
> 

Will look into it.

>> + *
>> + * This file define APIs for advanced power management,
>> + * which are architecture-dependent.
>> + */
>> +
>> +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change without prior notice
>> + *
>> + * Monitor specific address for changes. This will cause the CPU to enter an
>> + * architecture-defined optimized power state until either the specified
>> + * memory address is written to, a certain TSC timestamp is reached, or other
>> + * reasons cause the CPU to wake up.
>> + *
>> + * Additionally, an `expected` 64-bit value and 64-bit mask are provided. If
>> + * mask is non-zero, the current value pointed to by the `p` pointer will be
>> + * checked against the expected value, and if they match, the entering of
>> + * optimized power state may be aborted.
>> + *
>> + * @param p
>> + *   Address to monitor for changes. Must be aligned on an 64-byte boundary.
> 
> Is 64B alignment really needed?

I'm not 100% sure to be honest, but it's there just in case. I can 
remove it.

>>   'rte_prefetch.h',
>> +'rte_power_intrinsics.h',
>>   'rte_pause.h',
>>   'rte_rtm.h',
>>   'rte_rwlock.h',
>> diff --git a/lib/librte_eal/x86/include/rte_power_intrinsics.h b/lib/librte_eal/x86/include/rte_power_intrinsics.h
>> new file mode 100644
>> index 0000000000..9ac8e6eef6
>> --- /dev/null
>> +++ b/lib/librte_eal/x86/include/rte_power_intrinsics.h
>> @@ -0,0 +1,132 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(c) 2020 Intel Corporation
>> + */
>> +
>> +#ifndef _RTE_POWER_INTRINSIC_X86_64_H_
>> +#define _RTE_POWER_INTRINSIC_X86_64_H_
> 
> Why '_64_H'?
> My understanding was these ops are supported 32-bit mode too.

Yeah, artifact of early implementation. Will fix.

> 
>> +
>> +#ifdef __cplusplus
>> +extern "C" {
>> +#endif
>> +
>> +#include <rte_common.h>
>> +
>> +#include "generic/rte_power_intrinsics.h"
>> +
>> +static inline uint64_t __get_umwait_val(const volatile void *p,
>> +const uint8_t sz)
>> +{
>> +switch (sz) {
>> +case 1:
> 
> Just as a nit:
> case sizeof(type_x):
> return *(const volatile type_x *)p;

Thanks, will fix.

> 
>> +return *(const volatile uint8_t *)p;
>> +case 2:
>> +return *(const volatile uint16_t *)p;
>> +case 4:
>> +return *(const volatile uint32_t *)p;
>> +case 8:
>> +return *(const volatile uint64_t *)p;
>> +default:
>> +/* this is an intrinsic, so we can't have any error handling */
> 
> RTE_ASSERT(0); ?

Great idea, will add.
  

>>> +static inline void rte_power_monitor(const volatile void *p,
>>> +const uint64_t expected_value, const uint64_t value_mask,
>>> +const uint64_t tsc_timestamp, const uint8_t data_sz)
>>> +{
>>> +RTE_SET_USED(p);
>>> +RTE_SET_USED(expected_value);
>>> +RTE_SET_USED(value_mask);
>>> +RTE_SET_USED(tsc_timestamp);
>>> +RTE_SET_USED(data_sz);
>>> +}
>>
>> You can probably put NOP implementations of these rte_powe_* functions
>> into generic/rte_power_intrinsics.h.
>> So, wouldn't need to duplicate them for every non-supported arch.
>> Same as it was done for rte_wait_until_equal_*().
>>
> 
> Will look into it.
> 
To be completely honest, i don't like that approach. The ifdefery in 
generic headers looks ugly and out of place, i'd rather leave everything 
in arch specific header files and provide stubs there.