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From: "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>
To: <dev@dpdk.org>
Cc: nhorman@tuxdriver.com, stephen@networkplumber.org,
	david.marchand@redhat.com, bruce.richardson@intel.com,
	"Mattias Rönnblom" <mattias.ronnblom@ericsson.com>
Subject: [dpdk-dev] [PATCH 4/6] eal: introduce random generator function with upper bound
Date: Tue, 14 May 2019 11:20:44 +0200	[thread overview]
Message-ID: <20190514092046.30808-5-mattias.ronnblom@ericsson.com> (raw)
Message-ID: <20190514092044.gA-Fn8L6JFwJEVlWJvyAbouaJRzKea48_f0hO2g1vCc@z> (raw)
In-Reply-To: <20190514092046.30808-1-mattias.ronnblom@ericsson.com>

Add a function rte_rand_max() which generates an uniformly distributed
pseudo-random number less than a user-specified upper bound.

The commonly used pattern rte_rand() % SOME_VALUE creates biased
results (as in some values in the range are more frequently occurring
than others) if SOME_VALUE is not a power of 2.

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
---
 lib/librte_eal/common/include/rte_random.h | 18 ++++++++++
 lib/librte_eal/common/rte_random.c         | 39 ++++++++++++++++++++++
 lib/librte_eal/rte_eal_version.map         |  1 +
 3 files changed, 58 insertions(+)

diff --git a/lib/librte_eal/common/include/rte_random.h b/lib/librte_eal/common/include/rte_random.h
index 66dfe8ae7..939e6aaa9 100644
--- a/lib/librte_eal/common/include/rte_random.h
+++ b/lib/librte_eal/common/include/rte_random.h
@@ -17,6 +17,8 @@ extern "C" {
 
 #include <stdint.h>
 
+#include <rte_compat.h>
+
 /**
  * Seed the pseudo-random generator.
  *
@@ -47,6 +49,22 @@ rte_srand(uint64_t seedval);
 uint64_t
 rte_rand(void);
 
+/**
+ * Generates a pseudo-random number with an upper bound.
+ *
+ * This function returns an uniformly distributed (unbiased) random
+ * number less than a user-specified maximum value.
+ *
+ * If called from lcore threads, this function is thread-safe.
+ *
+ * @param upper_bound
+ *   The upper bound of the generated number.
+ * @return
+ *   A pseudo-random value between 0 and (upper_bound-1).
+ */
+uint64_t __rte_experimental
+rte_rand_max(uint64_t upper_bound);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/librte_eal/common/rte_random.c b/lib/librte_eal/common/rte_random.c
index aafc2f7ad..0e8abbb1c 100644
--- a/lib/librte_eal/common/rte_random.c
+++ b/lib/librte_eal/common/rte_random.c
@@ -134,6 +134,45 @@ rte_rand(void)
 	return __rte_rand_lfsr258(state);
 }
 
+uint64_t __rte_experimental
+rte_rand_max(uint64_t upper_bound)
+{
+	struct rte_rand_state *state;
+	uint8_t ones;
+	uint8_t leading_zeros;
+	uint64_t mask = ~((uint64_t)0);
+	uint64_t res;
+
+	if (unlikely(upper_bound < 2))
+		return 0;
+
+	state = __rte_rand_get_state();
+
+	ones = __builtin_popcountll(upper_bound);
+
+	/* Handle power-of-2 upper_bound as a special case, since it
+	 * has no bias issues.
+	 */
+	if (unlikely(ones == 1))
+		return __rte_rand_lfsr258(state) & (upper_bound - 1);
+
+	/* The approach to avoiding bias is to create a mask that
+	 * stretches beyond the request value range, and up to the
+	 * next power-of-2. In case the masked generated random value
+	 * is equal to or greater than the upper bound, just discard
+	 * the value and generate a new one.
+	 */
+
+	leading_zeros = __builtin_clzll(upper_bound);
+	mask >>= leading_zeros;
+
+	do {
+		res = __rte_rand_lfsr258(state) & mask;
+	} while (unlikely(res >= upper_bound));
+
+	return res;
+}
+
 RTE_INIT(rte_rand_init)
 {
 	uint64_t seed;
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index e615d7cb9..82483aed2 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -382,6 +382,7 @@ EXPERIMENTAL {
 	rte_mp_request_async;
 	rte_mp_sendmsg;
 	rte_option_register;
+	rte_rand_max;
 	rte_realloc_socket;
 	rte_service_lcore_attr_get;
 	rte_service_lcore_attr_reset_all;
-- 
2.17.1


  parent reply	other threads:[~2019-05-14  9:22 UTC|newest]

Thread overview: 137+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-05 13:45 [dpdk-dev] [RFC] eal: make rte_rand() MT safe Mattias Rönnblom
2019-04-05 13:45 ` Mattias Rönnblom
2019-04-05 13:51 ` Mattias Rönnblom
2019-04-05 13:51   ` Mattias Rönnblom
2019-04-05 14:28   ` Bruce Richardson
2019-04-05 14:28     ` Bruce Richardson
2019-04-05 14:56     ` Mattias Rönnblom
2019-04-05 14:56       ` Mattias Rönnblom
2019-04-05 16:57 ` Stephen Hemminger
2019-04-05 16:57   ` Stephen Hemminger
2019-04-05 18:04   ` Mattias Rönnblom
2019-04-05 18:04     ` Mattias Rönnblom
2019-04-05 20:50     ` Stephen Hemminger
2019-04-05 20:50       ` Stephen Hemminger
2019-04-06  5:52       ` Mattias Rönnblom
2019-04-06  5:52         ` Mattias Rönnblom
2019-04-08 12:30       ` [dpdk-dev] [RFC 1/3] Replace lrand48-based rte_rand with LFSR generator Mattias Rönnblom
2019-04-08 12:30         ` Mattias Rönnblom
2019-04-08 12:30         ` [dpdk-dev] [RFC 2/3] Add 32-bit version of rte_rand Mattias Rönnblom
2019-04-08 12:30           ` Mattias Rönnblom
2019-04-08 12:30         ` [dpdk-dev] [RFC 3/3] Introduce random generator functions with upper bound Mattias Rönnblom
2019-04-08 12:30           ` Mattias Rönnblom
2019-04-08 12:47         ` [dpdk-dev] [RFC 1/3] Replace lrand48-based rte_rand with LFSR generator Mattias Rönnblom
2019-04-08 12:47           ` Mattias Rönnblom
2019-04-19 21:21         ` [dpdk-dev] [RFC v2 0/2] Pseudo-number generation improvements Mattias Rönnblom
2019-04-19 21:21           ` Mattias Rönnblom
2019-04-19 21:21           ` [dpdk-dev] [RFC v2 1/2] eal: replace libc-based random number generation with LFSR Mattias Rönnblom
2019-04-19 21:21             ` Mattias Rönnblom
2019-04-22 11:34             ` Neil Horman
2019-04-22 11:34               ` Neil Horman
2019-04-22 14:49               ` Stephen Hemminger
2019-04-22 14:49                 ` Stephen Hemminger
2019-04-22 15:52               ` Mattias Rönnblom
2019-04-22 15:52                 ` Mattias Rönnblom
2019-04-22 17:44                 ` Mattias Rönnblom
2019-04-22 17:44                   ` Mattias Rönnblom
2019-04-23 11:33                   ` Neil Horman
2019-04-23 11:33                     ` Neil Horman
2019-04-23 17:13                     ` Mattias Rönnblom
2019-04-23 17:13                       ` Mattias Rönnblom
2019-04-24 11:37                       ` Neil Horman
2019-04-24 11:37                         ` Neil Horman
2019-04-23 15:31                   ` Stephen Hemminger
2019-04-23 15:31                     ` Stephen Hemminger
2019-04-23 17:17                     ` Mattias Rönnblom
2019-04-23 17:17                       ` Mattias Rönnblom
2019-04-24  7:52                       ` Mattias Rönnblom
2019-04-24  7:52                         ` Mattias Rönnblom
2019-04-24 12:33                         ` [dpdk-dev] [RFC v3 0/2] Pseudo-random number generation improvements Mattias Rönnblom
2019-04-24 12:33                           ` Mattias Rönnblom
2019-04-24 12:33                           ` [dpdk-dev] [RFC v3 1/2] eal: replace libc-based random number generation with LFSR Mattias Rönnblom
2019-04-24 12:33                             ` Mattias Rönnblom
2019-05-08 20:12                             ` Stephen Hemminger
2019-05-08 20:12                               ` Stephen Hemminger
2019-05-08 20:30                               ` Mattias Rönnblom
2019-05-08 20:30                                 ` Mattias Rönnblom
2019-05-09  1:10                                 ` Stephen Hemminger
2019-05-09  1:10                                   ` Stephen Hemminger
2019-05-14  9:20                                   ` [dpdk-dev] [PATCH 0/6] Pseudo-random number generation improvements Mattias Rönnblom
2019-05-14  9:20                                     ` Mattias Rönnblom
2019-05-14  9:20                                     ` [dpdk-dev] [PATCH 1/6] eal: replace libc-based random number generation with LFSR Mattias Rönnblom
2019-05-14  9:20                                       ` Mattias Rönnblom
2019-05-14  9:32                                       ` Mattias Rönnblom
2019-05-14  9:32                                         ` Mattias Rönnblom
2019-05-14 14:16                                       ` Neil Horman
2019-05-14 14:16                                         ` Neil Horman
2019-05-14 14:53                                         ` Mattias Rönnblom
2019-05-14 14:53                                           ` Mattias Rönnblom
2019-05-17 19:27                                           ` Neil Horman
2019-05-17 20:57                                             ` Bruce Richardson
2019-05-17 21:10                                             ` Mattias Rönnblom
2019-05-19 18:32                                               ` Neil Horman
2019-05-14 15:27                                       ` Stephen Hemminger
2019-05-14 15:27                                         ` Stephen Hemminger
2019-05-14  9:20                                     ` [dpdk-dev] [PATCH 2/6] eal: add pseudo-random number generation performance test Mattias Rönnblom
2019-05-14  9:20                                       ` Mattias Rönnblom
2019-05-14  9:20                                     ` [dpdk-dev] [PATCH 3/6] eal: improve entropy for initial PRNG seed Mattias Rönnblom
2019-05-14  9:20                                       ` Mattias Rönnblom
2019-05-14  9:36                                       ` Mattias Rönnblom
2019-05-14  9:36                                         ` Mattias Rönnblom
2019-05-14  9:39                                         ` Bruce Richardson
2019-05-14  9:39                                           ` Bruce Richardson
2019-05-14 11:58                                           ` Mattias Rönnblom
2019-05-14 11:58                                             ` Mattias Rönnblom
2019-05-14  9:37                                       ` Bruce Richardson
2019-05-14  9:37                                         ` Bruce Richardson
2019-05-14  9:20                                     ` Mattias Rönnblom [this message]
2019-05-14  9:20                                       ` [dpdk-dev] [PATCH 4/6] eal: introduce random generator function with upper bound Mattias Rönnblom
2019-05-14  9:20                                     ` [dpdk-dev] [PATCH 5/6] eal: add bounded PRNG performance tests Mattias Rönnblom
2019-05-14  9:20                                       ` Mattias Rönnblom
2019-05-14  9:20                                     ` [dpdk-dev] [PATCH 6/6] eal: add pseudo-random number generation to MAINTAINERS Mattias Rönnblom
2019-05-14  9:20                                       ` Mattias Rönnblom
2019-05-16 17:55                                     ` [dpdk-dev] [PATCH v2 0/6] Pseudo-random number generation improvements Mattias Rönnblom
2019-05-16 17:55                                       ` [dpdk-dev] [PATCH v2 1/6] eal: replace libc-based random number generation with LFSR Mattias Rönnblom
2019-05-16 17:55                                       ` [dpdk-dev] [PATCH v2 2/6] eal: add pseudo-random number generation performance test Mattias Rönnblom
2019-05-16 17:55                                       ` [dpdk-dev] [PATCH v2 3/6] eal: improve entropy for initial PRNG seed Mattias Rönnblom
2019-05-16 17:55                                       ` [dpdk-dev] [PATCH v2 4/6] eal: introduce random generator function with upper bound Mattias Rönnblom
2019-05-16 17:55                                       ` [dpdk-dev] [PATCH v2 5/6] eal: add bounded PRNG performance tests Mattias Rönnblom
2019-05-16 17:55                                       ` [dpdk-dev] [PATCH v2 6/6] eal: add PRNG to MAINTAINERS and release notes Mattias Rönnblom
2019-05-16 20:35                                       ` [dpdk-dev] [PATCH v2 0/6] Pseudo-random number generation improvements Bruce Richardson
2019-06-05 10:43                                         ` [dpdk-dev] [PATCH v3 " Mattias Rönnblom
2019-06-05 10:43                                           ` [dpdk-dev] [PATCH v3 1/6] eal: replace libc-based random number generation with LFSR Mattias Rönnblom
2019-06-05 10:43                                           ` [dpdk-dev] [PATCH v3 2/6] eal: add pseudo-random number generation performance test Mattias Rönnblom
2019-06-27 21:23                                             ` Thomas Monjalon
2019-06-28  8:20                                               ` Mattias Rönnblom
2019-06-05 10:43                                           ` [dpdk-dev] [PATCH v3 3/6] eal: improve entropy for initial PRNG seed Mattias Rönnblom
2019-06-05 10:43                                           ` [dpdk-dev] [PATCH v3 4/6] eal: introduce random generator function with upper bound Mattias Rönnblom
2019-06-05 10:43                                           ` [dpdk-dev] [PATCH v3 5/6] eal: add bounded PRNG performance tests Mattias Rönnblom
2019-06-05 10:44                                           ` [dpdk-dev] [PATCH v3 6/6] eal: add PRNG to MAINTAINERS and release notes Mattias Rönnblom
2019-06-27 21:27                                             ` Thomas Monjalon
2019-06-28  8:17                                               ` Mattias Rönnblom
2019-06-15 12:23                                           ` [dpdk-dev] [PATCH v3 0/6] Pseudo-random number generation improvements Mattias Rönnblom
2019-06-28  9:01                                           ` [dpdk-dev] [PATCH v4 0/5] " Mattias Rönnblom
2019-06-28  9:01                                             ` [dpdk-dev] [PATCH v4 1/5] eal: replace libc-based random number generation with LFSR Mattias Rönnblom
2019-06-28  9:01                                             ` [dpdk-dev] [PATCH v4 2/5] eal: add pseudo-random number generation performance test Mattias Rönnblom
2019-06-28  9:01                                             ` [dpdk-dev] [PATCH v4 3/5] eal: improve entropy for initial PRNG seed Mattias Rönnblom
2019-06-28 19:01                                               ` Ferruh Yigit
2019-06-28 20:58                                                 ` Mattias Rönnblom
2019-06-28 21:08                                                   ` [dpdk-dev] [PATCH] eal: use 32-bit RDSEED to allow 32-bit x86 usage Mattias Rönnblom
2019-06-29 12:54                                                     ` Thomas Monjalon
2019-06-28  9:01                                             ` [dpdk-dev] [PATCH v4 4/5] eal: introduce random generator function with upper bound Mattias Rönnblom
2019-06-28  9:01                                             ` [dpdk-dev] [PATCH v4 5/5] eal: add bounded PRNG performance tests Mattias Rönnblom
2019-06-28 13:24                                             ` [dpdk-dev] [PATCH v4 0/5] Pseudo-random number generation improvements Thomas Monjalon
2019-04-24 12:33                           ` [dpdk-dev] [RFC v3 2/2] eal: introduce random generator function with upper bound Mattias Rönnblom
2019-04-24 12:33                             ` Mattias Rönnblom
2019-04-19 21:21           ` [dpdk-dev] [RFC v2 " Mattias Rönnblom
2019-04-19 21:21             ` Mattias Rönnblom
2019-04-20 21:08             ` Wiles, Keith
2019-04-20 21:08               ` Wiles, Keith
2019-04-21 19:05               ` Mattias Rönnblom
2019-04-21 19:05                 ` Mattias Rönnblom
2019-04-22  4:33                 ` Wiles, Keith
2019-04-22  4:33                   ` Wiles, Keith
2019-04-22  7:07                   ` Mattias Rönnblom
2019-04-22  7:07                     ` Mattias Rönnblom
2019-04-22 13:19                     ` Wiles, Keith
2019-04-22 13:19                       ` Wiles, Keith

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