[dpdk-dev] [RFC] eal: make rte_rand() MT safe

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

The rte_rand() documentation left it unspecified if the rte_rand() was
multi-thread safe or not, and the implementation (based on lrand48())
was not.

This commit makes rte_rand() safe to use from any lcore thread by
using lrand48_r() and per-lcore random state structs. Besides the
obvious improvement in terms of correctness (for concurrent users),
this also much improves rte_rand() performance, since the threads no
longer shares state. For the single-threaded case, this patch causes
~10% rte_rand() performance degradation.

rte_srand() is left multi-thread unsafe, and external synchronization
is required to serialize rte_sand() calls from different lcore
threads, and a rte_srand() call with rte_rand() calls made by other
lcore threads.

The assumption is that the random number generators will be seeded
once, during startup.

Bugzilla ID: 114

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
---
 lib/librte_eal/common/include/rte_random.h | 25 ++++-----
 lib/librte_eal/common/meson.build          |  1 +
 lib/librte_eal/common/rte_random.c         | 65 ++++++++++++++++++++++
 lib/librte_eal/freebsd/eal/Makefile        |  1 +
 lib/librte_eal/freebsd/eal/eal.c           |  2 -
 lib/librte_eal/linux/eal/Makefile          |  1 +
 lib/librte_eal/linux/eal/eal.c             |  2 -
 lib/librte_eal/rte_eal_version.map         |  2 +
 8 files changed, 80 insertions(+), 19 deletions(-)
 create mode 100644 lib/librte_eal/common/rte_random.c

diff --git a/lib/librte_eal/common/include/rte_random.h b/lib/librte_eal/common/include/rte_random.h
index b2ca1c209..bca85a672 100644
--- a/lib/librte_eal/common/include/rte_random.h
+++ b/lib/librte_eal/common/include/rte_random.h
@@ -16,7 +16,6 @@ extern "C" {
 #endif
 
 #include <stdint.h>
-#include <stdlib.h>
 
 /**
  * Seed the pseudo-random generator.
@@ -25,14 +24,15 @@ extern "C" {
  * value. It may need to be re-seeded by the user with a real random
  * value.
  *
+ * This function is not multi-thread safe in regards to other
+ * rte_srand() calls, nor is it in relation to concurrent rte_rand()
+ * calls.
+ *
  * @param seedval
  *   The value of the seed.
  */
-static inline void
-rte_srand(uint64_t seedval)
-{
-	srand48((long)seedval);
-}
+void
+rte_srand(uint64_t seedval);
 
 /**
  * Get a pseudo-random value.
@@ -41,18 +41,13 @@ rte_srand(uint64_t seedval)
  * congruential algorithm and 48-bit integer arithmetic, called twice
  * to generate a 64-bit value.
  *
+ * If called from lcore threads, this function is thread-safe.
+ *
  * @return
  *   A pseudo-random value between 0 and (1<<64)-1.
  */
-static inline uint64_t
-rte_rand(void)
-{
-	uint64_t val;
-	val = (uint64_t)lrand48();
-	val <<= 32;
-	val += (uint64_t)lrand48();
-	return val;
-}
+uint64_t
+rte_rand(void);
 
 #ifdef __cplusplus
 }
diff --git a/lib/librte_eal/common/meson.build b/lib/librte_eal/common/meson.build
index 0670e4102..bafd23207 100644
--- a/lib/librte_eal/common/meson.build
+++ b/lib/librte_eal/common/meson.build
@@ -35,6 +35,7 @@ common_sources = files(
 	'rte_keepalive.c',
 	'rte_malloc.c',
 	'rte_option.c',
+	'rte_random.c',
 	'rte_reciprocal.c',
 	'rte_service.c'
 )
diff --git a/lib/librte_eal/common/rte_random.c b/lib/librte_eal/common/rte_random.c
new file mode 100644
index 000000000..9d519d03b
--- /dev/null
+++ b/lib/librte_eal/common/rte_random.c
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2010-2014 Intel Corporation
+ * Copyright(c) 2019 Ericsson AB
+ */
+
+#include <stdlib.h>
+
+#include <rte_cycles.h>
+#include <rte_eal.h>
+#include <rte_lcore.h>
+#include <rte_random.h>
+
+struct rte_rand_data
+{
+	struct drand48_data data;
+} __rte_cache_aligned;
+
+static struct rte_rand_data rand_data[RTE_MAX_LCORE];
+
+void
+rte_srand(uint64_t seedval)
+{
+	unsigned i;
+
+	/* give the different lcores a different seed, to avoid a
+	   situation where they generate the same sequence */
+	for (i = 0; i < RTE_MAX_LCORE; i++)
+		srand48_r((long)seedval + i, &rand_data[i].data);
+}
+
+static inline uint32_t
+__rte_rand48(struct drand48_data *data)
+{
+	long res;
+
+	lrand48_r(data, &res);
+
+	return (uint32_t)res;
+}
+
+uint64_t
+rte_rand(void)
+{
+	unsigned lcore_id;
+	struct drand48_data *data;
+	uint64_t val;
+
+	lcore_id = rte_lcore_id();
+
+	if (unlikely(lcore_id == LCORE_ID_ANY))
+		lcore_id = rte_get_master_lcore();
+
+	data = &rand_data[lcore_id].data;
+
+	val = __rte_rand48(data);
+	val <<= 32;
+	val += __rte_rand48(data);
+
+	return val;
+}
+
+RTE_INIT(rte_rand_init)
+{
+	rte_srand(rte_get_timer_cycles());
+}
diff --git a/lib/librte_eal/freebsd/eal/Makefile b/lib/librte_eal/freebsd/eal/Makefile
index 19854ee2c..ca616c480 100644
--- a/lib/librte_eal/freebsd/eal/Makefile
+++ b/lib/librte_eal/freebsd/eal/Makefile
@@ -69,6 +69,7 @@ SRCS-$(CONFIG_RTE_EXEC_ENV_FREEBSD) += malloc_mp.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_FREEBSD) += rte_keepalive.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_FREEBSD) += rte_option.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_FREEBSD) += rte_service.c
+SRCS-$(CONFIG_RTE_EXEC_ENV_FREEBSD) += rte_random.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_FREEBSD) += rte_reciprocal.c
 
 # from arch dir
diff --git a/lib/librte_eal/freebsd/eal/eal.c b/lib/librte_eal/freebsd/eal/eal.c
index c6ac9028f..5d43310b3 100644
--- a/lib/librte_eal/freebsd/eal/eal.c
+++ b/lib/librte_eal/freebsd/eal/eal.c
@@ -727,8 +727,6 @@ rte_eal_init(int argc, char **argv)
 #endif
 	}
 
-	rte_srand(rte_rdtsc());
-
 	/* in secondary processes, memory init may allocate additional fbarrays
 	 * not present in primary processes, so to avoid any potential issues,
 	 * initialize memzones first.
diff --git a/lib/librte_eal/linux/eal/Makefile b/lib/librte_eal/linux/eal/Makefile
index 6e5261152..729795a10 100644
--- a/lib/librte_eal/linux/eal/Makefile
+++ b/lib/librte_eal/linux/eal/Makefile
@@ -77,6 +77,7 @@ SRCS-$(CONFIG_RTE_EXEC_ENV_LINUX) += malloc_mp.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_LINUX) += rte_keepalive.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_LINUX) += rte_option.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_LINUX) += rte_service.c
+SRCS-$(CONFIG_RTE_EXEC_ENV_LINUX) += rte_random.c
 SRCS-$(CONFIG_RTE_EXEC_ENV_LINUX) += rte_reciprocal.c
 
 # from arch dir
diff --git a/lib/librte_eal/linux/eal/eal.c b/lib/librte_eal/linux/eal/eal.c
index f7ae62d7b..c2bdf0a67 100644
--- a/lib/librte_eal/linux/eal/eal.c
+++ b/lib/librte_eal/linux/eal/eal.c
@@ -1083,8 +1083,6 @@ rte_eal_init(int argc, char **argv)
 #endif
 	}
 
-	rte_srand(rte_rdtsc());
-
 	if (rte_eal_log_init(logid, internal_config.syslog_facility) < 0) {
 		rte_eal_init_alert("Cannot init logging.");
 		rte_errno = ENOMEM;
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index d6e375135..0d60668fa 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -366,10 +366,12 @@ EXPERIMENTAL {
 	rte_mp_request_async;
 	rte_mp_sendmsg;
 	rte_option_register;
+	rte_rand;
 	rte_realloc_socket;
 	rte_service_lcore_attr_get;
 	rte_service_lcore_attr_reset_all;
 	rte_service_may_be_active;
 	rte_socket_count;
 	rte_socket_id_by_idx;
+	rte_srand;
 };
-- 
2.17.1