[dpdk-dev] [PATCH v10 2/5] eal: add the APIs to wait until equal

Gavin Hu gavin.hu at arm.com
Fri Oct 25 17:39:08 CEST 2019


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.hu at arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
Reviewed-by: Steve Capper <steve.capper at arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl at arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
Reviewed-by: Phil Yang <phil.yang at arm.com>
Acked-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
Acked-by: Jerin Jacob <jerinj at marvell.com>
---
 config/arm/meson.build                             |   1 +
 config/common_base                                 |   5 +
 .../common/include/arch/arm/rte_pause_64.h         | 188 +++++++++++++++++++++
 lib/librte_eal/common/include/generic/rte_pause.h  | 108 ++++++++++++
 4 files changed, 302 insertions(+)

diff --git a/config/arm/meson.build b/config/arm/meson.build
index 979018e..b4b4cac 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 e843a21..c812156 100644
--- a/config/common_base
+++ b/config/common_base
@@ -111,6 +111,11 @@ 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/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..dd37f72 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 +23,188 @@ static inline void rte_pause(void)
 	asm volatile("yield" ::: "memory");
 }
 
+/**
+ * Send an event to exit WFE.
+ */
+static inline void rte_sevl(void);
+
+/**
+ * Put processor into low power WFE(Wait For Event) state
+ */
+static inline void rte_wfe(void);
+
+#ifdef RTE_ARM_USE_WFE
+static inline void rte_sevl(void)
+{
+	asm volatile("sevl" : : : "memory");
+}
+
+static inline void rte_wfe(void)
+{
+	asm volatile("wfe" : : : "memory");
+}
+#else
+static inline void rte_sevl(void)
+{
+}
+static inline void rte_wfe(void)
+{
+	rte_pause();
+}
+#endif
+
+#ifdef RTE_WAIT_UNTIL_EQUAL_ARCH_DEFINED
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
+ *
+ * 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.
+ *
+ * @param addr
+ *  A pointer to the memory location.
+ * @param memorder
+ *  The valid memory order variants are __ATOMIC_ACQUIRE and __ATOMIC_RELAXED.
+ *  These map to C++11 memory orders with the same names, see the C++11 standard
+ *  the GCC wiki on atomic synchronization for detailed definitions.
+ */
+static __rte_always_inline uint16_t
+__atomic_load_ex_16(volatile uint16_t *addr, int memorder);
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
+ *
+ * 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.
+ *
+ * @param addr
+ *  A pointer to the memory location.
+ * @param memorder
+ *  The valid memory order variants are __ATOMIC_ACQUIRE and __ATOMIC_RELAXED.
+ *  These map to C++11 memory orders with the same names, see the C++11 standard
+ *  the GCC wiki on atomic synchronization for detailed definitions.
+ */
+static __rte_always_inline uint32_t
+__atomic_load_ex_32(volatile uint32_t *addr, int memorder);
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
+ *
+ * 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.
+ *
+ * @param addr
+ *  A pointer to the memory location.
+ * @param memorder
+ *  The valid memory order variants are __ATOMIC_ACQUIRE and __ATOMIC_RELAXED.
+ *  These map to C++11 memory orders with the same names, see the C++11 standard
+ *  the GCC wiki on atomic synchronization for detailed definitions.
+ */
+static __rte_always_inline uint64_t
+__atomic_load_ex_64(volatile uint64_t *addr, int memorder);
+
+static __rte_always_inline uint16_t
+__atomic_load_ex_16(volatile uint16_t *addr, int memorder)
+{
+	uint16_t tmp;
+	assert((memorder == __ATOMIC_ACQUIRE)
+			|| (memorder == __ATOMIC_RELAXED));
+	if (memorder == __ATOMIC_ACQUIRE)
+		asm volatile("ldaxrh %w[tmp], [%x[addr]]"
+			: [tmp] "=&r" (tmp)
+			: [addr] "r"(addr)
+			: "memory");
+	else if (memorder == __ATOMIC_RELAXED)
+		asm volatile("ldxrh %w[tmp], [%x[addr]]"
+			: [tmp] "=&r" (tmp)
+			: [addr] "r"(addr)
+			: "memory");
+	return tmp;
+}
+
+static __rte_always_inline uint32_t
+__atomic_load_ex_32(volatile uint32_t *addr, int memorder)
+{
+	uint32_t tmp;
+	assert((memorder == __ATOMIC_ACQUIRE)
+			|| (memorder == __ATOMIC_RELAXED));
+	if (memorder == __ATOMIC_ACQUIRE)
+		asm volatile("ldaxr %w[tmp], [%x[addr]]"
+			: [tmp] "=&r" (tmp)
+			: [addr] "r"(addr)
+			: "memory");
+	else if (memorder == __ATOMIC_RELAXED)
+		asm volatile("ldxr %w[tmp], [%x[addr]]"
+			: [tmp] "=&r" (tmp)
+			: [addr] "r"(addr)
+			: "memory");
+	return tmp;
+}
+
+static __rte_always_inline uint64_t
+__atomic_load_ex_64(volatile uint64_t *addr, int memorder)
+{
+	uint64_t tmp;
+	assert((memorder == __ATOMIC_ACQUIRE)
+			|| (memorder == __ATOMIC_RELAXED));
+	if (memorder == __ATOMIC_ACQUIRE)
+		asm volatile("ldaxr %x[tmp], [%x[addr]]"
+			: [tmp] "=&r" (tmp)
+			: [addr] "r"(addr)
+			: "memory");
+	else if (memorder == __ATOMIC_RELAXED)
+		asm volatile("ldxr %x[tmp], [%x[addr]]"
+			: [tmp] "=&r" (tmp)
+			: [addr] "r"(addr)
+			: "memory");
+	return tmp;
+}
+
+static __rte_always_inline void
+rte_wait_until_equal_16(volatile uint16_t *addr, uint16_t expected,
+int memorder)
+{
+	if (__atomic_load_n(addr, memorder) != expected) {
+		rte_sevl();
+		do {
+			rte_wfe();
+		} while (__atomic_load_ex_16(addr, memorder) != expected);
+	}
+}
+
+static __rte_always_inline void
+rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected,
+int memorder)
+{
+	if (__atomic_load_n(addr, memorder) != expected) {
+		rte_sevl();
+		do {
+			rte_wfe();
+		} while (__atomic_load_n(addr, memorder) != expected);
+	}
+}
+
+static __rte_always_inline void
+rte_wait_until_equal_64(volatile uint64_t *addr, uint64_t expected,
+int memorder)
+{
+	if (__atomic_load_n(addr, memorder) != expected) {
+		rte_sevl();
+		do {
+			rte_wfe();
+		} while (__atomic_load_n(addr, memorder) != expected);
+	}
+}
+#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..9854455 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 <rte_common.h>
+#include <rte_atomic.h>
+#include <rte_compat.h>
+#include <assert.h>
+
 /**
  * Pause CPU execution for a short while
  *
@@ -20,4 +27,105 @@
  */
 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)
+{
+	if (__atomic_load_n(addr, memorder) != expected) {
+		do {
+			rte_pause();
+		} while (__atomic_load_n(addr, memorder) != expected);
+	}
+}
+
+static __rte_always_inline void
+rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected,
+int memorder)
+{
+	if (__atomic_load_n(addr, memorder) != expected) {
+		do {
+			rte_pause();
+		} while (__atomic_load_n(addr, memorder) != expected);
+	}
+}
+
+static __rte_always_inline void
+rte_wait_until_equal_64(volatile uint64_t *addr, uint64_t expected,
+int memorder)
+{
+	if (__atomic_load_n(addr, memorder) != expected) {
+		do {
+			rte_pause();
+		} while (__atomic_load_n(addr, memorder) != expected);
+	}
+}
+#endif
+
 #endif /* _RTE_PAUSE_H_ */
-- 
2.7.4



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