[dpdk-dev] [PATCH v7 1/3] eal/ticketlock: ticket based to improve fairness

[Joyce Kong <joyce.kong@arm.com>]

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@marvell.com>
Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
---
 MAINTAINERS                                        |   4 +
 doc/api/doxy-api-index.md                          |   1 +
 lib/librte_eal/common/Makefile                     |   2 +-
 .../common/include/generic/rte_ticketlock.h        | 215 +++++++++++++++++++++
 lib/librte_eal/common/meson.build                  |   1 +
 5 files changed, 222 insertions(+), 1 deletion(-)
 create mode 100644 lib/librte_eal/common/include/generic/rte_ticketlock.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 452b8eb..3521271 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -210,6 +210,10 @@ M: Cristian Dumitrescu <cristian.dumitrescu@intel.com>
 F: lib/librte_eal/common/include/rte_bitmap.h
 F: app/test/test_bitmap.c
 
+Ticketlock
+M: Joyce Kong <joyce.kong@arm.com>
+F: lib/librte_eal/common/include/generic/rte_ticketlock.h
+
 ARM v7
 M: Jan Viktorin <viktorin@rehivetech.com>
 M: Gavin Hu <gavin.hu@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 c487201..ac3305c 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..c5203cb
--- /dev/null
+++ b/lib/librte_eal/common/include/generic/rte_ticketlock.h
@@ -0,0 +1,215 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 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.
+ *
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <rte_common.h>
+#include <rte_lcore.h>
+#include <rte_pause.h>
+
+/**
+ * The rte_ticketlock_t type.
+ */
+typedef union {
+	uint32_t tickets;
+	struct {
+		uint16_t current;
+		uint16_t next;
+	} s;
+} 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->tickets, 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)
+{
+	uint16_t me = __atomic_fetch_add(&tl->s.next, 1, __ATOMIC_RELAXED);
+	while (__atomic_load_n(&tl->s.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)
+{
+	uint16_t i = __atomic_load_n(&tl->s.current, __ATOMIC_RELAXED);
+	__atomic_store_n(&tl->s.current, i + 1, __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)
+{
+	rte_ticketlock_t old, new;
+	old.tickets = __atomic_load_n(&tl->tickets, __ATOMIC_RELAXED);
+	new.tickets = __atomic_load_n(&tl->tickets, __ATOMIC_RELAXED);
+	new.s.next++;
+	if (old.s.next == old.s.current) {
+		if (__atomic_compare_exchange_n(&tl->tickets, &old.tickets,
+		    new.tickets, 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 is currently taken; 0 otherwise.
+ */
+static inline __rte_experimental int
+rte_ticketlock_is_locked(rte_ticketlock_t *tl)
+{
+	rte_ticketlock_t tic;
+	tic.tickets = __atomic_load_n(&tl->tickets, __ATOMIC_ACQUIRE);
+	return (tic.s.current != tic.s.next);
+}
+
+/**
+ * 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, \
+					       TICKET_LOCK_INVALID_ID, 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);
+	tlr->count = 0;
+}
+
+/**
+ * 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;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_TICKETLOCK_H_ */
diff --git a/lib/librte_eal/common/meson.build b/lib/librte_eal/common/meson.build
index 5ecae0b..0670e41 100644
--- a/lib/librte_eal/common/meson.build
+++ b/lib/librte_eal/common/meson.build
@@ -99,6 +99,7 @@ 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