This is a new type of reader-writer lock that provides better fairness
guarantees. According to the research it will be better for real
time applications such as DPDK.
A similar implementation is Concurrency Kit available in FreeBSD.
For information see:
"Reader-Writer Synchronization for Shared-Memory Multiprocessor
Real-Time Systems",
http://www.cs.unc.edu/~anderson/papers/ecrts09b.pdf
Signed-off-by: Stephen Hemminger <sthem...@microsoft.com>
---
Note: This is better than earlier ticket variant proposal so dropping
that one. The fairness properties are better.
app/test/meson.build | 6 +
app/test/test_pflock.c | 220 ++++++++++++++++
lib/librte_eal/arm/include/meson.build | 1 +
lib/librte_eal/arm/include/rte_pflock.h | 18 ++
lib/librte_eal/include/generic/rte_pflock.h | 272 ++++++++++++++++++++
lib/librte_eal/ppc/include/meson.build | 1 +
lib/librte_eal/ppc/include/rte_pflock.h | 16 ++
lib/librte_eal/x86/include/meson.build | 1 +
lib/librte_eal/x86/include/rte_pflock.h | 18 ++
9 files changed, 553 insertions(+)
create mode 100644 app/test/test_pflock.c
create mode 100644 lib/librte_eal/arm/include/rte_pflock.h
create mode 100644 lib/librte_eal/include/generic/rte_pflock.h
create mode 100644 lib/librte_eal/ppc/include/rte_pflock.h
create mode 100644 lib/librte_eal/x86/include/rte_pflock.h
diff --git a/app/test/meson.build b/app/test/meson.build
index 94fd39fecb82..d5cf0ba701e9 100644
--- a/app/test/meson.build
+++ b/app/test/meson.build
@@ -89,6 +89,7 @@ test_sources = files('commands.c',
'test_mcslock.c',
'test_mp_secondary.c',
'test_per_lcore.c',
+ 'test_pflock.c',
'test_pmd_perf.c',
'test_power.c',
'test_power_cpufreq.c',
@@ -227,6 +228,11 @@ fast_tests = [
['meter_autotest', true],
['multiprocess_autotest', false],
['per_lcore_autotest', true],
+ ['pflock_autotest', true],
+ ['pflock_test1_autotest', true],
+ ['pflock_rda_autotest', true],
+ ['pflock_rds_wrm_autotest', true],
+ ['pflock_rde_wro_autotest', true],
['prefetch_autotest', true],
['rcu_qsbr_autotest', true],
['red_autotest', true],
diff --git a/app/test/test_pflock.c b/app/test/test_pflock.c
new file mode 100644
index 000000000000..b6c5d2f8afde
--- /dev/null
+++ b/app/test/test_pflock.c
@@ -0,0 +1,220 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2010-2014 Intel Corporation
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <unistd.h>
+#include <sys/queue.h>
+#include <string.h>
+
+#include <rte_common.h>
+#include <rte_memory.h>
+#include <rte_per_lcore.h>
+#include <rte_launch.h>
+#include <rte_pause.h>
+#include <rte_pflock.h>
+#include <rte_eal.h>
+#include <rte_lcore.h>
+#include <rte_cycles.h>
+
+#include "test.h"
+
+/*
+ * phase fair lock test
+ * ===========
+ * Provides UT for phase fair lock API.
+ * Main concern is on functional testing, but also provides some
+ * performance measurements.
+ * Obviously for proper testing need to be executed with more than one lcore.
+ */
+
+#define ITER_NUM 0x80
+
+#define TEST_SEC 5
+
+static rte_pflock_t sl;
+static rte_pflock_t sl_tab[RTE_MAX_LCORE];
+static uint32_t synchro;
+
+enum {
+ LC_TYPE_RDLOCK,
+ LC_TYPE_WRLOCK,
+};
+
+static int
+test_pflock_per_core(__rte_unused void *arg)
+{
+ rte_pflock_write_lock(&sl);
+ printf("Global write lock taken on core %u\n", rte_lcore_id());
+ rte_pflock_write_unlock(&sl);
+
+ rte_pflock_write_lock(&sl_tab[rte_lcore_id()]);
+ printf("Hello from core %u !\n", rte_lcore_id());
+ rte_pflock_write_unlock(&sl_tab[rte_lcore_id()]);
+
+ rte_pflock_read_lock(&sl);
+ printf("Global read lock taken on core %u\n", rte_lcore_id());
+ rte_delay_ms(100);
+ printf("Release global read lock on core %u\n", rte_lcore_id());
+ rte_pflock_read_unlock(&sl);
+
+ return 0;
+}
+
+static rte_pflock_t lk = RTE_PFLOCK_INITIALIZER;
+static volatile uint64_t pflock_data;
+static uint64_t time_count[RTE_MAX_LCORE] = {0};
+
+#define MAX_LOOP 10000
+#define TEST_PFLOCK_DEBUG 0
+
+static int
+load_loop_fn(__rte_unused void *arg)
+{
+ uint64_t time_diff = 0, begin;
+ uint64_t hz = rte_get_timer_hz();
+ uint64_t lcount = 0;
+ const unsigned int lcore = rte_lcore_id();
+
+ /* wait synchro for workers */
+ if (lcore != rte_get_main_lcore())
+ rte_wait_until_equal_32(&synchro, 1, __ATOMIC_RELAXED);
+
+ begin = rte_rdtsc_precise();
+ while (lcount < MAX_LOOP) {
+ rte_pflock_write_lock(&lk);
+ ++pflock_data;
+ rte_pflock_write_unlock(&lk);
+
+ rte_pflock_read_lock(&lk);
+ if (TEST_PFLOCK_DEBUG && !(lcount % 100))
+ printf("Core [%u] pflock_data = %"PRIu64"\n",
+ lcore, pflock_data);
+ rte_pflock_read_unlock(&lk);
+
+ lcount++;
+ /* delay to make lock duty cycle slightly realistic */
+ rte_pause();
+ }
+
+ time_diff = rte_rdtsc_precise() - begin;
+ time_count[lcore] = time_diff * 1000000 / hz;
+ return 0;
+}
+
+static int
+test_pflock_perf(void)
+{
+ unsigned int i;
+ uint64_t total = 0;
+
+ printf("\nPhase fair test on %u cores...\n", rte_lcore_count());
+
+ /* clear synchro and start workers */
+ synchro = 0;
+ if (rte_eal_mp_remote_launch(load_loop_fn, NULL, SKIP_MAIN) < 0)
+ return -1;
+
+ /* start synchro and launch test on main */
+ __atomic_store_n(&synchro, 1, __ATOMIC_RELAXED);
+ load_loop_fn(NULL);
+
+ rte_eal_mp_wait_lcore();
+
+ RTE_LCORE_FOREACH(i) {
+ printf("Core [%u] cost time = %"PRIu64" us\n",
+ i, time_count[i]);
+ total += time_count[i];
+ }
+
+ printf("Total cost time = %"PRIu64" us\n", total);
+ memset(time_count, 0, sizeof(time_count));
+
+ return 0;
+}
+
+/*
+ * - There is a global pflock and a table of pflocks (one per lcore).
+ *
+ * - The test function takes all of these locks and launches the
+ * ``test_pflock_per_core()`` function on each core (except the main).
+ *
+ * - The function takes the global write lock, display something,
+ * then releases the global lock.
+ * - Then, it takes the per-lcore write lock, display something, and
+ * releases the per-core lock.
+ * - Finally, a read lock is taken during 100 ms, then released.
+ *
+ * - The main function unlocks the per-lcore locks sequentially and
+ * waits between each lock. This triggers the display of a message
+ * for each core, in the correct order.
+ *
+ * Then, it tries to take the global write lock and display the last
+ * message. The autotest script checks that the message order is correct.
+ */
+static int
+pflock_test1(void)
+{
+ int i;
+
+ rte_pflock_init(&sl);
+ for (i = 0; i < RTE_MAX_LCORE; i++)
+ rte_pflock_init(&sl_tab[i]);
+
+ rte_pflock_write_lock(&sl);
+
+ RTE_LCORE_FOREACH_WORKER(i) {
+ rte_pflock_write_lock(&sl_tab[i]);
+ rte_eal_remote_launch(test_pflock_per_core, NULL, i);
+ }
+
+ rte_pflock_write_unlock(&sl);
+
+ RTE_LCORE_FOREACH_WORKER(i) {
+ rte_pflock_write_unlock(&sl_tab[i]);
+ rte_delay_ms(100);
+ }
+
+ rte_pflock_write_lock(&sl);
+ /* this message should be the last message of test */
+ printf("Global write lock taken on main core %u\n", rte_lcore_id());
+ rte_pflock_write_unlock(&sl);
+
+ rte_eal_mp_wait_lcore();
+
+ if (test_pflock_perf() < 0)
+ return -1;
+
+ return 0;
+}
+
+static int
+test_pflock(void)
+{
+ uint32_t i;
+ int32_t rc, ret;
+
+ static const struct {
+ const char *name;
+ int (*ftst)(void);
+ } test[] = {
+ {
+ .name = "pflock_test1",
+ .ftst = pflock_test1,
+ },
+ };
+
+ ret = 0;
+ for (i = 0; i != RTE_DIM(test); i++) {
+ printf("starting test %s;\n", test[i].name);
+ rc = test[i].ftst();
+ printf("test %s completed with status %d\n", test[i].name, rc);
+ ret |= rc;
+ }
+
+ return ret;
+}
+
+REGISTER_TEST_COMMAND(pflock_autotest, test_pflock);
diff --git a/lib/librte_eal/arm/include/meson.build
b/lib/librte_eal/arm/include/meson.build
index 770766de1a34..2c3cff61bed6 100644
--- a/lib/librte_eal/arm/include/meson.build
+++ b/lib/librte_eal/arm/include/meson.build
@@ -21,6 +21,7 @@ arch_headers = files(
'rte_pause_32.h',
'rte_pause_64.h',
'rte_pause.h',
+ 'rte_pflock.h',
'rte_power_intrinsics.h',
'rte_prefetch_32.h',
'rte_prefetch_64.h',
diff --git a/lib/librte_eal/arm/include/rte_pflock.h
b/lib/librte_eal/arm/include/rte_pflock.h
new file mode 100644
index 000000000000..bb9934eec469
--- /dev/null
+++ b/lib/librte_eal/arm/include/rte_pflock.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2021 Microsoft Corporation
+ */
+
+#ifndef _RTE_PFLOCK_ARM_H_
+#define _RTE_PFLOCK_ARM_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "generic/rte_pflock.h"
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_PFLOCK_ARM_H_ */
diff --git a/lib/librte_eal/include/generic/rte_pflock.h
b/lib/librte_eal/include/generic/rte_pflock.h
new file mode 100644
index 000000000000..afa4edeb2830
--- /dev/null
+++ b/lib/librte_eal/include/generic/rte_pflock.h
@@ -0,0 +1,272 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2021 Microsoft Corp.
+ * Copyright 2011-2015 Samy Al Bahra.
+ * All rights reserved.
+ */
+
+#ifndef _RTE_PFLOCK_H_
+#define _RTE_PFLOCK_H_
+
+/**
+ * @file
+ *
+ * Phase-fair locks
+ *
+ * This file defines an API for Phase Fair reader writer locks,
+ * which is a variant of typical reader-writer locks that prevent
+ * starvation. In this type of lock, readers and writers alternate.
+ * This significantly reduces the worst-case blocking for readers and writers.
+ *
+ * This is an implementation derived from FreeBSD
+ * based on the work described in:
+ * Brandenburg, B. and Anderson, J. 2010. Spin-Based
+ * Reader-Writer Synchronization for Multiprocessor Real-Time Systems
+ *
+ * All locks must be initialised before use, and only initialised once.
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <rte_common.h>
+#include <rte_pause.h>
+
+/**
+ * The rte_pflock_t type.
+ */
+struct rte_pflock {
+ union rte_pflock_ticket {
+ uint32_t tickets;
+ struct {
+ uint16_t in;
+ uint16_t out;
+ };
+ } rd, wr;
+};
+typedef struct rte_pflock rte_pflock_t;
+
+/**
+ * Constants used to map the bits in reader counter
+ *
+ * +-----------------+-+-+
+ * | Readers |W|P|
+ * | |R|H|
+ * +-----------------+-+-+
+ */
+#define RTE_PFLOCK_LSB 0xFFFFFFF0
+#define RTE_PFLOCK_RINC 0x100 /* Reader increment value. */
+#define RTE_PFLOCK_WBITS 0x3 /* Writer bits in reader. */
+#define RTE_PFLOCK_PRES 0x2 /* Writer present bit. */
+#define RTE_PFLOCK_PHID 0x1 /* Phase ID bit. */
+
+/**
+ * A static pflock initializer.
+ */
+#define RTE_PFLOCK_INITIALIZER { }
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Initialize the pflock to an unlocked state.
+ *
+ * @param pf
+ * A pointer to the pflock.
+ */
+__rte_experimental
+static inline void
+rte_pflock_init(struct rte_pflock *pf)
+{
+ pf->rd.tickets = 0;
+ pf->wr.tickets = 0;
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Take a pflock for read.
+ *
+ * @param pf
+ * A pointer to a pflock structure.
+ */
+__rte_experimental
+static inline void
+rte_pflock_read_lock(rte_pflock_t *pf)
+{
+ uint32_t w;
+
+ /*
+ * If no writer is present, then the operation has completed
+ * successfully.
+ */
+ w = __atomic_fetch_add(&pf->rd.in, RTE_PFLOCK_RINC, __ATOMIC_ACQ_REL) &
RTE_PFLOCK_WBITS;
+ if (w == 0)
+ return;
+
+ /* Wait for current write phase to complete. */
+ while ((__atomic_load_n(&pf->rd.in, __ATOMIC_ACQUIRE) &
RTE_PFLOCK_WBITS) == w)
+ rte_pause();
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Release a pflock locked for reading.
+ *
+ * @param pf
+ * A pointer to the pflock structure.
+ */
+__rte_experimental
+static inline void
+rte_pflock_read_unlock(rte_pflock_t *pf)
+{
+ __atomic_fetch_add(&pf->rd.out, RTE_PFLOCK_RINC, __ATOMIC_RELEASE);
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Try to take a pflock for reading
+ *
+ * @param pf
+ * A pointer to a pflock structure.
+ * @return
+ * - zero if the lock is successfully taken
+ * - -EBUSY if lock could not be acquired for reading because a
+ * writer holds the lock
+ */
+__rte_experimental
+static inline int
+rte_pflock_read_trylock(rte_pflock_t *pf)
+{
+ union rte_pflock_ticket old, new;
+
+ /* Get current state of the lock */
+ old.tickets = __atomic_load_n(&pf->rd.tickets, __ATOMIC_RELAXED);
+
+ /* loop until writer shows up */
+ while ((old.in & RTE_PFLOCK_WBITS) == 0) {
+ new.out = old.out;
+ new.in = old.in + RTE_PFLOCK_RINC;
+ if (__atomic_compare_exchange_n(&pf->rd.tickets, &old.tickets,
new.tickets,
+ 0, __ATOMIC_ACQ_REL,
__ATOMIC_RELAXED))
+ return 0; /* got it */
+
+ /* either new reader got in (so retry) or a writer */
+ }
+
+ /* If writer is present then we are busy */
+ return -EBUSY;
+}
+
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Take the pflock for write.
+ *
+ * @param p
+ * A pointer to the ticketlock.
+ */
+__rte_experimental
+static inline void
+rte_pflock_write_lock(rte_pflock_t *pf)
+{
+ uint16_t ticket;
+
+ /* Acquire ownership of write-phase. */
+ ticket = __atomic_fetch_add(&pf->wr.in, 1, __ATOMIC_ACQUIRE);
+ rte_wait_until_equal_16(&pf->wr.out, ticket, __ATOMIC_RELAXED);
+
+ /*
+ * Acquire ticket on read-side in order to allow them
+ * to flush. Indicates to any incoming reader that a
+ * write-phase is pending.
+ *
+ * Need ACQUIRE to prevent speculative execution of the wait loop
+ */
+ ticket = __atomic_fetch_add(&pf->rd.in,
+ (ticket & RTE_PFLOCK_PHID) |
RTE_PFLOCK_PRES,
+ __ATOMIC_ACQUIRE);
+
+ /* Wait for any pending readers to flush. */
+ rte_wait_until_equal_16(&pf->rd.out, ticket, __ATOMIC_RELAXED);
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Release a pflock held for writing.
+ *
+ * @param pf
+ * A pointer to a pflock structure.
+ */
+__rte_experimental
+static inline void
+rte_pflock_write_unlock(rte_pflock_t *pf)
+{
+ /* Migrate from write phase to read phase. */
+ __atomic_fetch_and(&pf->rd.in, RTE_PFLOCK_LSB, __ATOMIC_RELEASE);
+
+ /* Allow other writers to continue. */
+ __atomic_fetch_add(&pf->wr.out, 1, __ATOMIC_RELEASE);
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Try to take the pflock for write.
+ *
+ * @param pf
+ * A pointer to the pflock.
+ * @return
+ * - zero if the lock is successfully taken
+ * - -EBUSY if lock could not be acquired for writing because
+ * another writer holds the lock
+ */
+__rte_experimental
+static inline int
+rte_pflock_write_trylock(rte_pflock_t *pf)
+{
+ union rte_pflock_ticket old, new;
+ uint16_t ticket;
+
+ /* Get current state of the lock */
+ old.tickets = __atomic_load_n(&pf->wr.tickets, __ATOMIC_RELAXED);
+ new.out = old.out;
+ new.in = old.in + 1;
+ ticket = new.in;
+
+ /* if writer is already present then too busy */
+ if (old.out != new.in ||
+ !__atomic_compare_exchange_n(&pf->wr.tickets, &old.tickets,
new.tickets,
+ 0, __ATOMIC_ACQ_REL, __ATOMIC_RELAXED))
+ return -EBUSY; /* another writer is present already */
+
+ /*
+ * We now own the write phase, but still need to tell
+ * readers and wait for them.
+ *
+ * Need ACQUIRE semantics to avoid speculative execution of wait loop
+ */
+ ticket = __atomic_fetch_add(&pf->rd.in,
+ (ticket & RTE_PFLOCK_PHID) | RTE_PFLOCK_PRES,
+ __ATOMIC_ACQUIRE);
+
+ /* Wait for any pending readers to flush. */
+ rte_wait_until_equal_16(&pf->rd.out, ticket, __ATOMIC_RELAXED);
+ return 0;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* RTE_PFLOCK_H */
diff --git a/lib/librte_eal/ppc/include/meson.build
b/lib/librte_eal/ppc/include/meson.build
index dae40ede546e..7692a531ccba 100644
--- a/lib/librte_eal/ppc/include/meson.build
+++ b/lib/librte_eal/ppc/include/meson.build
@@ -11,6 +11,7 @@ arch_headers = files(
'rte_mcslock.h',
'rte_memcpy.h',
'rte_pause.h',
+ 'rte_pflock.h',
'rte_power_intrinsics.h',
'rte_prefetch.h',
'rte_rwlock.h',
diff --git a/lib/librte_eal/ppc/include/rte_pflock.h
b/lib/librte_eal/ppc/include/rte_pflock.h
new file mode 100644
index 000000000000..e7b875ac56a8
--- /dev/null
+++ b/lib/librte_eal/ppc/include/rte_pflock.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ */
+#ifndef _RTE_PFLOCK_PPC_64_H_
+#define _RTE_PFLOCK_PPC_64_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "generic/rte_pflock.h"
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_PFLOCK_PPC_64_H_ */
diff --git a/lib/librte_eal/x86/include/meson.build
b/lib/librte_eal/x86/include/meson.build
index 549cc21a42ed..39222cf724be 100644
--- a/lib/librte_eal/x86/include/meson.build
+++ b/lib/librte_eal/x86/include/meson.build
@@ -14,6 +14,7 @@ arch_headers = files(
'rte_mcslock.h',
'rte_memcpy.h',
'rte_pause.h',
+ 'rte_pflock.h',
'rte_power_intrinsics.h',
'rte_prefetch.h',
'rte_rtm.h',
diff --git a/lib/librte_eal/x86/include/rte_pflock.h
b/lib/librte_eal/x86/include/rte_pflock.h
new file mode 100644
index 000000000000..c2d876062c08
--- /dev/null
+++ b/lib/librte_eal/x86/include/rte_pflock.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2021 Microsoft Corporation
+ */
+
+#ifndef _RTE_PFLOCK_X86_64_H_
+#define _RTE_PFLOCK_X86_64_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "generic/rte_pflock.h"
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_PFLOCK_X86_64_H_ */
--
2.30.0
