[dpdk-dev] [PATCH v4 1/2] ticketlock: ticket based to improve fairness

Joyce Kong joyce.kong at arm.com
Tue Feb 19 11:48:07 CET 2019


The spinlock implementation is unfair, some threads may take locks
aggressively while leaving the other threads starving for long time.

This patch introduces ticketlock which gives each waiting thread a
ticket and they can take the lock one by one. First come, first serviced.
This avoids starvation for too long time and is more predictable.

Suggested-by: Jerin Jacob <jerinj at marvell.com>
Signed-off-by: Joyce kong <joyce.kong at arm.com>
Reviewed-by: Gavin Hu <gavin.hu at arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl at arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
---
 MAINTAINERS                                        |   4 +
 doc/api/doxy-api-index.md                          |   1 +
 lib/librte_eal/common/Makefile                     |   2 +-
 .../common/include/generic/rte_ticketlock.h        | 201 +++++++++++++++++++++
 lib/librte_eal/common/meson.build                  |   1 +
 5 files changed, 208 insertions(+), 1 deletion(-)
 create mode 100644 lib/librte_eal/common/include/generic/rte_ticketlock.h

diff --git a/MAINTAINERS b/MAINTAINERS
index eef480a..022e6bb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -212,6 +212,10 @@ M: Cristian Dumitrescu <cristian.dumitrescu at intel.com>
 F: lib/librte_eal/common/include/rte_bitmap.h
 F: test/test/test_bitmap.c
 
+Ticketlock
+M: Joyce Kong <joyce.kong at arm.com>
+F: lib/librte_eal/common/include/generic/rte_ticketlock.h
+
 ARM v7
 M: Jan Viktorin <viktorin at rehivetech.com>
 M: Gavin Hu <gavin.hu at arm.com>
diff --git a/doc/api/doxy-api-index.md b/doc/api/doxy-api-index.md
index d95ad56..aacc66b 100644
--- a/doc/api/doxy-api-index.md
+++ b/doc/api/doxy-api-index.md
@@ -65,6 +65,7 @@ The public API headers are grouped by topics:
   [atomic]             (@ref rte_atomic.h),
   [rwlock]             (@ref rte_rwlock.h),
   [spinlock]           (@ref rte_spinlock.h)
+  [ticketlock]         (@ref rte_ticketlock.h)
 
 - **CPU arch**:
   [branch prediction]  (@ref rte_branch_prediction.h),
diff --git a/lib/librte_eal/common/Makefile b/lib/librte_eal/common/Makefile
index 87d8c45..99e948b 100644
--- a/lib/librte_eal/common/Makefile
+++ b/lib/librte_eal/common/Makefile
@@ -20,7 +20,7 @@ INC += rte_bitmap.h rte_vfio.h rte_hypervisor.h rte_test.h
 INC += rte_reciprocal.h rte_fbarray.h rte_uuid.h
 
 GENERIC_INC := rte_atomic.h rte_byteorder.h rte_cycles.h rte_prefetch.h
-GENERIC_INC += rte_spinlock.h rte_memcpy.h rte_cpuflags.h rte_rwlock.h
+GENERIC_INC += rte_spinlock.h rte_memcpy.h rte_cpuflags.h rte_rwlock.h rte_ticketlock.h
 GENERIC_INC += rte_vect.h rte_pause.h rte_io.h
 
 # defined in mk/arch/$(RTE_ARCH)/rte.vars.mk
diff --git a/lib/librte_eal/common/include/generic/rte_ticketlock.h b/lib/librte_eal/common/include/generic/rte_ticketlock.h
new file mode 100644
index 0000000..4846962
--- /dev/null
+++ b/lib/librte_eal/common/include/generic/rte_ticketlock.h
@@ -0,0 +1,201 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2018-2019 Arm Limited
+ */
+
+#ifndef _RTE_TICKETLOCK_H_
+#define _RTE_TICKETLOCK_H_
+
+/**
+ * @file
+ *
+ * RTE ticket locks
+ *
+ * This file defines an API for ticket locks, which give each waiting
+ * thread a ticket and take the lock one by one, first come, first
+ * serviced.
+ *
+ * All locks must be initialised before use, and only initialised once.
+ *
+ */
+
+#include <rte_lcore.h>
+#include <rte_common.h>
+#include <rte_pause.h>
+
+/**
+ * The rte_ticketlock_t type.
+ */
+typedef struct {
+	unsigned int current;
+	unsigned int next;
+} rte_ticketlock_t;
+
+/**
+ * A static ticketlock initializer.
+ */
+#define RTE_TICKETLOCK_INITIALIZER { 0 }
+
+/**
+ * Initialize the ticketlock to an unlocked state.
+ *
+ * @param tl
+ *   A pointer to the ticketlock.
+ */
+static inline __rte_experimental void
+rte_ticketlock_init(rte_ticketlock_t *tl)
+{
+	__atomic_store_n(&tl->current, 0, __ATOMIC_RELAXED);
+	__atomic_store_n(&tl->next, 0, __ATOMIC_RELAXED);
+}
+
+/**
+ * Take the ticketlock.
+ *
+ * @param tl
+ *   A pointer to the ticketlock.
+ */
+static inline __rte_experimental void
+rte_ticketlock_lock(rte_ticketlock_t *tl)
+{
+	unsigned int me = __atomic_fetch_add(&tl->next, 1, __ATOMIC_RELAXED);
+	while (__atomic_load_n(&tl->current, __ATOMIC_ACQUIRE) != me)
+		rte_pause();
+}
+
+/**
+ * Release the ticketlock.
+ *
+ * @param tl
+ *   A pointer to the ticketlock.
+ */
+static inline __rte_experimental void
+rte_ticketlock_unlock(rte_ticketlock_t *tl)
+{
+	unsigned int i = __atomic_load_n(&tl->current, __ATOMIC_RELAXED);
+	i++;
+	__atomic_store_n(&tl->current, i, __ATOMIC_RELEASE);
+}
+
+/**
+ * Try to take the lock.
+ *
+ * @param tl
+ *   A pointer to the ticketlock.
+ * @return
+ *   1 if the lock is successfully taken; 0 otherwise.
+ */
+static inline __rte_experimental int
+rte_ticketlock_trylock(rte_ticketlock_t *tl)
+{
+	unsigned int next = __atomic_load_n(&tl->next, __ATOMIC_RELAXED);
+	unsigned int cur = __atomic_load_n(&tl->current, __ATOMIC_RELAXED);
+	if (next == cur) {
+		if (__atomic_compare_exchange_n(&tl->next, &next, next+1,
+			0, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
+			return 1;
+	}
+
+	return 0;
+}
+
+/**
+ * Test if the lock is taken.
+ *
+ * @param tl
+ *   A pointer to the ticketlock.
+ * @return
+ *   1 if the lock icurrently taken; 0 otherwise.
+ */
+static inline __rte_experimental int
+rte_ticketlock_is_locked(rte_ticketlock_t *tl)
+{
+	return (__atomic_load_n(&tl->current, __ATOMIC_ACQUIRE) !=
+			__atomic_load_n(&tl->next, __ATOMIC_ACQUIRE));
+}
+
+/**
+ * The rte_ticketlock_recursive_t type.
+ */
+#define TICKET_LOCK_INVALID_ID -1
+
+typedef struct {
+	rte_ticketlock_t tl; /**< the actual ticketlock */
+	int user; /**< core id using lock, TICKET_LOCK_INVALID_ID for unused */
+	unsigned int count; /**< count of time this lock has been called */
+} rte_ticketlock_recursive_t;
+
+/**
+ * A static recursive ticketlock initializer.
+ */
+#define RTE_TICKETLOCK_RECURSIVE_INITIALIZER {RTE_TICKETLOCK_INITIALIZER, -1, 0}
+
+/**
+ * Initialize the recursive ticketlock to an unlocked state.
+ *
+ * @param tlr
+ *   A pointer to the recursive ticketlock.
+ */
+static inline __rte_experimental void
+rte_ticketlock_recursive_init(rte_ticketlock_recursive_t *tlr)
+{
+	rte_ticketlock_init(&tlr->tl);
+	__atomic_store_n(&tlr->user, TICKET_LOCK_INVALID_ID, __ATOMIC_RELAXED);
+	__atomic_store_n(&tlr->count, 0, __ATOMIC_RELAXED);
+}
+
+/**
+ * Take the recursive ticketlock.
+ *
+ * @param tlr
+ *   A pointer to the recursive ticketlock.
+ */
+static inline __rte_experimental void
+rte_ticketlock_recursive_lock(rte_ticketlock_recursive_t *tlr)
+{
+	int id = rte_gettid();
+
+	if (__atomic_load_n(&tlr->user, __ATOMIC_RELAXED) != id) {
+		rte_ticketlock_lock(&tlr->tl);
+		__atomic_store_n(&tlr->user, id, __ATOMIC_RELAXED);
+	}
+	tlr->count++;
+}
+
+/**
+ * Release the recursive ticketlock.
+ *
+ * @param tlr
+ *   A pointer to the recursive ticketlock.
+ */
+static inline __rte_experimental void
+rte_ticketlock_recursive_unlock(rte_ticketlock_recursive_t *tlr)
+{
+	if (--(tlr->count) == 0) {
+		__atomic_store_n(&tlr->user, TICKET_LOCK_INVALID_ID, __ATOMIC_RELAXED);
+		rte_ticketlock_unlock(&tlr->tl);
+	}
+}
+
+/**
+ * Try to take the recursive lock.
+ *
+ * @param tlr
+ *   A pointer to the recursive ticketlock.
+ * @return
+ *   1 if the lock is successfully taken; 0 otherwise.
+ */
+static inline __rte_experimental int
+rte_ticketlock_recursive_trylock(rte_ticketlock_recursive_t *tlr)
+{
+	int id = rte_gettid();
+
+	if (__atomic_load_n(&tlr->user, __ATOMIC_RELAXED) != id) {
+		if (rte_ticketlock_trylock(&tlr->tl) == 0)
+			return 0;
+		__atomic_store_n(&tlr->user, id, __ATOMIC_RELAXED);
+	}
+	tlr->count++;
+	return 1;
+}
+
+#endif /* _RTE_TICKETLOCK_H_ */
diff --git a/lib/librte_eal/common/meson.build b/lib/librte_eal/common/meson.build
index 2a10d57..23f9416 100644
--- a/lib/librte_eal/common/meson.build
+++ b/lib/librte_eal/common/meson.build
@@ -98,6 +98,7 @@ generic_headers = files(
 	'include/generic/rte_prefetch.h',
 	'include/generic/rte_rwlock.h',
 	'include/generic/rte_spinlock.h',
+	'include/generic/rte_ticketlock.h',
 	'include/generic/rte_vect.h')
 install_headers(generic_headers, subdir: 'generic')
 
-- 
2.7.4



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