[dpdk-dev] [PATCH 1/6] eal: replace libc-based random number generation with LFSR

Mattias Rönnblom mattias.ronnblom at ericsson.com
Tue May 14 11:20:41 CEST 2019


This commit replaces rte_rand()'s use of lrand48() with a DPDK-native
combined Linear Feedback Shift Register (LFSR) (also known as
Tausworthe) pseudo-random number generator.

This generator is faster and produces better-quality random numbers
than the linear congruential generator (LCG) of lib's lrand48(). The
implementation, as opposed to lrand48(), is multi-thread safe in
regards to concurrent rte_rand() calls from different lcore threads.
A LCG is still used, but only to seed the five per-lcore LFSR
sequences.

In addition, this patch also addresses the issue of the legacy
implementation only producing 62 bits of pseudo randomness, while the
API requires all 64 bits to be random.

This pseudo-random number generator is not cryptographically secure -
just like lrand48().

Bugzilla ID: 114
Bugzilla ID: 276

Signed-off-by: Mattias Rönnblom <mattias.ronnblom at ericsson.com>
---
 lib/librte_eal/common/include/rte_random.h |  29 ++---
 lib/librte_eal/common/meson.build          |   1 +
 lib/librte_eal/common/rte_random.c         | 139 +++++++++++++++++++++
 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         |   8 ++
 8 files changed, 161 insertions(+), 22 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..66dfe8ae7 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.
@@ -25,34 +24,28 @@ 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.
  *
- * This function generates pseudo-random numbers using the linear
- * congruential algorithm and 48-bit integer arithmetic, called twice
- * to generate a 64-bit value.
+ * The generator is not cryptographically secure.
+ *
+ * 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..4d3cf5226
--- /dev/null
+++ b/lib/librte_eal/common/rte_random.c
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2019 Ericsson AB
+ */
+
+#include <stdlib.h>
+
+#include <rte_branch_prediction.h>
+#include <rte_cycles.h>
+#include <rte_eal.h>
+#include <rte_lcore.h>
+#include <rte_memory.h>
+#include <rte_random.h>
+
+struct rte_rand_state {
+	uint64_t z1;
+	uint64_t z2;
+	uint64_t z3;
+	uint64_t z4;
+	uint64_t z5;
+} __rte_cache_aligned;
+
+static struct rte_rand_state rand_states[RTE_MAX_LCORE];
+
+static uint32_t
+__rte_rand_lcg32(uint32_t *seed)
+{
+	*seed = 1103515245U * *seed + 12345U;
+
+	return *seed;
+}
+
+static uint64_t
+__rte_rand_lcg64(uint32_t *seed)
+{
+	uint64_t low;
+	uint64_t high;
+
+	/* A 64-bit LCG would have been much cleaner, but good
+	 * multiplier/increments for such seem hard to come by.
+	 */
+
+	low = __rte_rand_lcg32(seed);
+	high = __rte_rand_lcg32(seed);
+
+	return low | (high << 32);
+}
+
+static uint64_t
+__rte_rand_lfsr258_gen_seed(uint32_t *seed, uint64_t min_value)
+{
+	uint64_t res;
+
+	res = __rte_rand_lcg64(seed);
+
+	if (res < min_value)
+		res += min_value;
+
+	return res;
+}
+
+static void
+__rte_srand_lfsr258(uint64_t seed, struct rte_rand_state *state)
+{
+	uint32_t lcg_seed;
+
+	lcg_seed = (uint32_t)(seed ^ (seed >> 32));
+
+	state->z1 = __rte_rand_lfsr258_gen_seed(&lcg_seed, 2UL);
+	state->z2 = __rte_rand_lfsr258_gen_seed(&lcg_seed, 512UL);
+	state->z3 = __rte_rand_lfsr258_gen_seed(&lcg_seed, 4096UL);
+	state->z4 = __rte_rand_lfsr258_gen_seed(&lcg_seed, 131072UL);
+	state->z5 = __rte_rand_lfsr258_gen_seed(&lcg_seed, 8388608UL);
+}
+
+void
+rte_srand(uint64_t seed)
+{
+	unsigned int lcore_id;
+
+	/* add lcore_id to seed to avoid having the same sequence */
+	for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++)
+		__rte_srand_lfsr258(seed + lcore_id, &rand_states[lcore_id]);
+}
+
+static __rte_always_inline uint64_t
+__rte_rand_lfsr258_comp(uint64_t z, uint64_t a, uint64_t b, uint64_t c,
+			uint64_t d)
+{
+	return ((z & c) << d) ^ (((z << a) ^ z) >> b);
+}
+
+/* Based on L’Ecuyer, P.: Tables of maximally equidistributed combined
+ * LFSR generators.
+ */
+
+static __rte_always_inline uint64_t
+__rte_rand_lfsr258(struct rte_rand_state *state)
+{
+	state->z1 = __rte_rand_lfsr258_comp(state->z1, 1UL, 53UL,
+					    18446744073709551614UL, 10UL);
+	state->z2 = __rte_rand_lfsr258_comp(state->z2, 24UL, 50UL,
+					    18446744073709551104UL, 5UL);
+	state->z3 = __rte_rand_lfsr258_comp(state->z3, 3UL, 23UL,
+					    18446744073709547520UL, 29UL);
+	state->z4 = __rte_rand_lfsr258_comp(state->z4, 5UL, 24UL,
+					    18446744073709420544UL, 23UL);
+	state->z5 = __rte_rand_lfsr258_comp(state->z5, 3UL, 33UL,
+					    18446744073701163008UL, 8UL);
+
+	return state->z1 ^ state->z2 ^ state->z3 ^ state->z4 ^ state->z5;
+}
+
+static __rte_always_inline
+struct rte_rand_state *__rte_rand_get_state(void)
+{
+	unsigned int lcore_id;
+
+	lcore_id = rte_lcore_id();
+
+	if (unlikely(lcore_id == LCORE_ID_ANY))
+		lcore_id = rte_get_master_lcore();
+
+	return &rand_states[lcore_id];
+}
+
+uint64_t
+rte_rand(void)
+{
+	struct rte_rand_state *state;
+
+	state = __rte_rand_get_state();
+
+	return __rte_rand_lfsr258(state);
+}
+
+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 161399619..d6bf0e89e 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 245493461..e615d7cb9 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -287,6 +287,14 @@ DPDK_19.05 {
 
 } DPDK_18.11;
 
+DPDK_19.08 {
+	global:
+
+	rte_rand;
+	rte_srand;
+
+} DPDK_19.05;
+
 EXPERIMENTAL {
 	global:
 
-- 
2.17.1



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