Hi David,
> From: Gavin Hu <gavin...@arm.com>
>
> The rte_wait_until_equal_xx APIs abstract the functionality of
> 'polling for a memory location to become equal to a given value'.
>
> Add the RTE_ARM_USE_WFE configuration entry for aarch64, disabled
> by default. When it is enabled, the above APIs will call WFE instruction
> to save CPU cycles and power.
>
> From a VM, when calling this API on aarch64, it may trap in and out to
> release vCPUs whereas cause high exit latency. Since kernel 4.18.20 an
> adaptive trapping mechanism is introduced to balance the latency and
> workload.
>
> Signed-off-by: Gavin Hu <gavin...@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
> Reviewed-by: Steve Capper <steve.cap...@arm.com>
> Reviewed-by: Ola Liljedahl <ola.liljed...@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> Reviewed-by: Phil Yang <phil.y...@arm.com>
> Acked-by: Pavan Nikhilesh <pbhagavat...@marvell.com>
> Acked-by: Jerin Jacob <jer...@marvell.com>
> Acked-by: Konstantin Ananyev <konstantin.anan...@intel.com>
> Signed-off-by: David Marchand <david.march...@redhat.com>
> ---
> Changelog since v12:
> - added release notes update,
> - fixed function prototypes indent,
> - reimplemented the arm implementation without exposing internal inline
> functions,
> - added asserts in generic implementation,
>
> ---
> config/arm/meson.build | 1 +
> config/common_base | 5 +
> doc/guides/rel_notes/release_19_11.rst | 5 +
> .../common/include/arch/arm/rte_pause_64.h | 133
> +++++++++++++++++++++
> lib/librte_eal/common/include/generic/rte_pause.h | 105 ++++++++++++++++
> 5 files changed, 249 insertions(+)
>
> diff --git a/config/arm/meson.build b/config/arm/meson.build
> index 46dff3a..ea47425 100644
> --- a/config/arm/meson.build
> +++ b/config/arm/meson.build
> @@ -26,6 +26,7 @@ flags_common_default = [
> ['RTE_LIBRTE_AVP_PMD', false],
>
> ['RTE_SCHED_VECTOR', false],
> + ['RTE_ARM_USE_WFE', false],
> ]
>
> flags_generic = [
> diff --git a/config/common_base b/config/common_base
> index 1858598..bb1b1ed 100644
> --- a/config/common_base
> +++ b/config/common_base
> @@ -110,6 +110,11 @@ CONFIG_RTE_MAX_VFIO_CONTAINERS=64
> CONFIG_RTE_MALLOC_DEBUG=n
> CONFIG_RTE_EAL_NUMA_AWARE_HUGEPAGES=n
> CONFIG_RTE_USE_LIBBSD=n
> +# Use WFE instructions to implement the rte_wait_for_equal_xxx APIs,
> +# calling these APIs put the cores in low power state while waiting
> +# for the memory address to become equal to the expected value.
> +# This is supported only by aarch64.
> +CONFIG_RTE_ARM_USE_WFE=n
>
> #
> # Recognize/ignore the AVX/AVX512 CPU flags for performance/power testing.
> diff --git a/doc/guides/rel_notes/release_19_11.rst
> b/doc/guides/rel_notes/release_19_11.rst
> index fe11b4b..af5f2c5 100644
> --- a/doc/guides/rel_notes/release_19_11.rst
> +++ b/doc/guides/rel_notes/release_19_11.rst
> @@ -65,6 +65,11 @@ New Features
>
> The lock-free stack implementation is enabled for aarch64 platforms.
>
> +* **Added Wait Until Equal API.**
> +
> + A new API has been added to wait for a memory location to be updated with a
> + 16-bit, 32-bit, 64-bit value.
> +
> * **Changed mempool allocation behaviour.**
>
> Objects are no longer across pages by default.
> diff --git a/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> b/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> index 93895d3..e87d10b 100644
> --- a/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> +++ b/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> @@ -1,5 +1,6 @@
> /* SPDX-License-Identifier: BSD-3-Clause
> * Copyright(c) 2017 Cavium, Inc
> + * Copyright(c) 2019 Arm Limited
> */
>
> #ifndef _RTE_PAUSE_ARM64_H_
> @@ -10,6 +11,11 @@ extern "C" {
> #endif
>
> #include <rte_common.h>
> +
> +#ifdef RTE_ARM_USE_WFE
> +#define RTE_WAIT_UNTIL_EQUAL_ARCH_DEFINED
> +#endif
> +
> #include "generic/rte_pause.h"
>
> static inline void rte_pause(void)
> @@ -17,6 +23,133 @@ static inline void rte_pause(void)
> asm volatile("yield" ::: "memory");
> }
>
> +#ifdef RTE_WAIT_UNTIL_EQUAL_ARCH_DEFINED
> +
> +/* Send an event to quit WFE. */
> +#define __SEVL() { asm volatile("sevl" : : : "memory"); }
> +
> +/* Put processor into low power WFE(Wait For Event) state. */
> +#define __WFE() { asm volatile("wfe" : : : "memory"); }
> +
> +static __rte_always_inline void
> +rte_wait_until_equal_16(volatile uint16_t *addr, uint16_t expected,
> + int memorder)
> +{
> + uint16_t value;
> +
> + assert(memorder == __ATOMIC_ACQUIRE || memorder == __ATOMIC_RELAXED);
> +
> + /*
> + * Atomic exclusive load from addr, it returns the 16-bit content of
> + * *addr while making it 'monitored',when it is written by someone
> + * else, the 'monitored' state is cleared and a event is generated
> + * implicitly to exit WFE.
> + */
> +#define __LOAD_EXC_16(src, dst, memorder) { \
> + if (memorder == __ATOMIC_RELAXED) { \
> + asm volatile("ldxrh %w[tmp], [%x[addr]]" \
> + : [tmp] "=&r" (dst) \
> + : [addr] "r"(src) \
> + : "memory"); \
> + } else { \
> + asm volatile("ldaxrh %w[tmp], [%x[addr]]" \
> + : [tmp] "=&r" (dst) \
> + : [addr] "r"(src) \
> + : "memory"); \
> + } }
> +
> + __LOAD_EXC_16(addr, value, memorder)
> + if (value != expected) {
> + __SEVL()
> + do {
> + __WFE()
> + __LOAD_EXC_16(addr, value, memorder)
> + } while (value != expected);
> + }
> +#undef __LOAD_EXC_16
> +}
> +
> +static __rte_always_inline void
> +rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected,
> + int memorder)
> +{
> + uint32_t value;
> +
> + assert(memorder == __ATOMIC_ACQUIRE || memorder == __ATOMIC_RELAXED);
> +
> + /*
> + * Atomic exclusive load from addr, it returns the 32-bit content of
> + * *addr while making it 'monitored',when it is written by someone
> + * else, the 'monitored' state is cleared and a event is generated
> + * implicitly to exit WFE.
> + */
> +#define __LOAD_EXC_32(src, dst, memorder) { \
> + if (memorder == __ATOMIC_RELAXED) { \
> + asm volatile("ldxr %w[tmp], [%x[addr]]" \
> + : [tmp] "=&r" (dst) \
> + : [addr] "r"(src) \
> + : "memory"); \
> + } else { \
> + asm volatile("ldaxr %w[tmp], [%x[addr]]" \
> + : [tmp] "=&r" (dst) \
> + : [addr] "r"(src) \
> + : "memory"); \
> + } }
> +
> + __LOAD_EXC_32(addr, value, memorder)
> + if (value != expected) {
> + __SEVL()
> + do {
> + __WFE()
> + __LOAD_EXC_32(addr, value, memorder)
> + } while (value != expected);
> + }
> +#undef __LOAD_EXC_32
> +}
> +
> +static __rte_always_inline void
> +rte_wait_until_equal_64(volatile uint64_t *addr, uint64_t expected,
> + int memorder)
> +{
> + uint64_t value;
> +
> + assert(memorder == __ATOMIC_ACQUIRE || memorder == __ATOMIC_RELAXED);
> +
> + /*
> + * Atomic exclusive load from addr, it returns the 64-bit content of
> + * *addr while making it 'monitored',when it is written by someone
> + * else, the 'monitored' state is cleared and a event is generated
> + * implicitly to exit WFE.
> + */
> +#define __LOAD_EXC_64(src, dst, memorder) { \
> + if (memorder == __ATOMIC_RELAXED) { \
> + asm volatile("ldxr %x[tmp], [%x[addr]]" \
> + : [tmp] "=&r" (dst) \
> + : [addr] "r"(src) \
> + : "memory"); \
> + } else { \
> + asm volatile("ldaxr %x[tmp], [%x[addr]]" \
> + : [tmp] "=&r" (dst) \
> + : [addr] "r"(src) \
> + : "memory"); \
> + } }
> +
> + __LOAD_EXC_64(addr, value, memorder)
> + if (value != expected) {
> + __SEVL()
> + do {
> + __WFE()
> + __LOAD_EXC_64(addr, value, memorder)
> + } while (value != expected);
> + }
> +}
> +#undef __LOAD_EXC_64
> +
> +#undef __SEVL
> +#undef __WFE
Personally I don't see how these define/undef are better then inline
functions...
Again I suppose they might be re-used in future some other ARM specific
low-level primitvies.
My preference would be to keep them as inline function - much cleaner code.
But as I don't develop for/use, I wouldn't insist and let you and arm guys to
decide.
Konstantin
> +
> +#endif
> +
> #ifdef __cplusplus
> }
> #endif
> diff --git a/lib/librte_eal/common/include/generic/rte_pause.h
> b/lib/librte_eal/common/include/generic/rte_pause.h
> index 52bd4db..7422785 100644
> --- a/lib/librte_eal/common/include/generic/rte_pause.h
> +++ b/lib/librte_eal/common/include/generic/rte_pause.h
> @@ -1,5 +1,6 @@
> /* SPDX-License-Identifier: BSD-3-Clause
> * Copyright(c) 2017 Cavium, Inc
> + * Copyright(c) 2019 Arm Limited
> */
>
> #ifndef _RTE_PAUSE_H_
> @@ -12,6 +13,12 @@
> *
> */
>
> +#include <stdint.h>
> +#include <assert.h>
> +#include <rte_common.h>
> +#include <rte_atomic.h>
> +#include <rte_compat.h>
> +
> /**
> * Pause CPU execution for a short while
> *
> @@ -20,4 +27,102 @@
> */
> static inline void rte_pause(void);
>
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
> + *
> + * Wait for *addr to be updated with a 16-bit expected value, with a relaxed
> + * memory ordering model meaning the loads around this API can be reordered.
> + *
> + * @param addr
> + * A pointer to the memory location.
> + * @param expected
> + * A 16-bit expected value to be in the memory location.
> + * @param memorder
> + * Two different memory orders that can be specified:
> + * __ATOMIC_ACQUIRE and __ATOMIC_RELAXED. These map to
> + * C++11 memory orders with the same names, see the C++11 standard or
> + * the GCC wiki on atomic synchronization for detailed definition.
> + */
> +__rte_experimental
> +static __rte_always_inline void
> +rte_wait_until_equal_16(volatile uint16_t *addr, uint16_t expected,
> + int memorder);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
> + *
> + * Wait for *addr to be updated with a 32-bit expected value, with a relaxed
> + * memory ordering model meaning the loads around this API can be reordered.
> + *
> + * @param addr
> + * A pointer to the memory location.
> + * @param expected
> + * A 32-bit expected value to be in the memory location.
> + * @param memorder
> + * Two different memory orders that can be specified:
> + * __ATOMIC_ACQUIRE and __ATOMIC_RELAXED. These map to
> + * C++11 memory orders with the same names, see the C++11 standard or
> + * the GCC wiki on atomic synchronization for detailed definition.
> + */
> +__rte_experimental
> +static __rte_always_inline void
> +rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected,
> + int memorder);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
> + *
> + * Wait for *addr to be updated with a 64-bit expected value, with a relaxed
> + * memory ordering model meaning the loads around this API can be reordered.
> + *
> + * @param addr
> + * A pointer to the memory location.
> + * @param expected
> + * A 64-bit expected value to be in the memory location.
> + * @param memorder
> + * Two different memory orders that can be specified:
> + * __ATOMIC_ACQUIRE and __ATOMIC_RELAXED. These map to
> + * C++11 memory orders with the same names, see the C++11 standard or
> + * the GCC wiki on atomic synchronization for detailed definition.
> + */
> +__rte_experimental
> +static __rte_always_inline void
> +rte_wait_until_equal_64(volatile uint64_t *addr, uint64_t expected,
> + int memorder);
> +
> +#ifndef RTE_WAIT_UNTIL_EQUAL_ARCH_DEFINED
> +static __rte_always_inline void
> +rte_wait_until_equal_16(volatile uint16_t *addr, uint16_t expected,
> + int memorder)
> +{
> + assert(memorder == __ATOMIC_ACQUIRE || memorder == __ATOMIC_RELAXED);
> +
> + while (__atomic_load_n(addr, memorder) != expected)
> + rte_pause();
> +}
> +
> +static __rte_always_inline void
> +rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected,
> + int memorder)
> +{
> + assert(memorder == __ATOMIC_ACQUIRE || memorder == __ATOMIC_RELAXED);
> +
> + while (__atomic_load_n(addr, memorder) != expected)
> + rte_pause();
> +}
> +
> +static __rte_always_inline void
> +rte_wait_until_equal_64(volatile uint64_t *addr, uint64_t expected,
> + int memorder)
> +{
> + assert(memorder == __ATOMIC_ACQUIRE || memorder == __ATOMIC_RELAXED);
> +
> + while (__atomic_load_n(addr, memorder) != expected)
> + rte_pause();
> +}
> +#endif
> +
> #endif /* _RTE_PAUSE_H_ */
> --
> 1.8.3.1
