From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by dpdk.space (Postfix) with ESMTP id C36E9A05D3 for ; Wed, 24 Apr 2019 14:33:44 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id B1F361B4E3; Wed, 24 Apr 2019 14:33:39 +0200 (CEST) Received: from sesbmg22.ericsson.net (sesbmg22.ericsson.net [193.180.251.48]) by dpdk.org (Postfix) with ESMTP id 9A1B71B2B0 for ; Wed, 24 Apr 2019 14:33:37 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; d=ericsson.com; s=mailgw201801; c=relaxed/relaxed; q=dns/txt; i=@ericsson.com; t=1556109217; x=1558701217; h=From:Sender:Reply-To:Subject:Date:Message-ID:To:CC:MIME-Version:Content-Type: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=mVt6qNT+KVb8TgSEPSLAqv4/01tiUkrrU+5bjs//QJ8=; b=E5IiUjgIiKHArPagpefqOUQH8pTNSy2csls1y06+363Y41Ccodn+39P51hcDCpJ3 9pi1fn/nPkwLHfSPi/YueiaESzASxmxNx0jBwHS+4gQ2qXlmR63/UL1TzReDRKrn F6hoalFTaBbZSLnrPt4QXuDKwGwt9D0b4AMmcZCIzE4=; X-AuditID: c1b4fb30-6ddff70000001814-07-5cc057a15456 Received: from ESESBMB501.ericsson.se (Unknown_Domain [153.88.183.114]) by sesbmg22.ericsson.net (Symantec Mail Security) with SMTP id 67.F3.06164.1A750CC5; Wed, 24 Apr 2019 14:33:37 +0200 (CEST) Received: from ESESBMB502.ericsson.se (153.88.183.169) by ESESBMB501.ericsson.se (153.88.183.168) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1713.5; Wed, 24 Apr 2019 14:33:36 +0200 Received: from selio1a020.lmera.ericsson.se (153.88.183.153) by smtp.internal.ericsson.com (153.88.183.185) with Microsoft SMTP Server id 15.1.1713.5 via Frontend Transport; Wed, 24 Apr 2019 14:33:36 +0200 Received: from breslau.lmera.ericsson.se (breslau.lmera.ericsson.se [150.132.109.241]) by selio1a020.lmera.ericsson.se (8.15.1+Sun/8.15.1) with ESMTP id x3OCXNAe010622; Wed, 24 Apr 2019 14:33:36 +0200 (CEST) From: =?UTF-8?q?Mattias=20R=C3=B6nnblom?= To: CC: , , =?UTF-8?q?Mattias=20R=C3=B6nnblom?= Date: Wed, 24 Apr 2019 14:33:20 +0200 Message-ID: <20190424123320.19610-3-mattias.ronnblom@ericsson.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190424123320.19610-1-mattias.ronnblom@ericsson.com> References: <20190424123320.19610-1-mattias.ronnblom@ericsson.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFrrGLMWRmVeSWpSXmKPExsUyM2J7ke7C8AMxBot/8Vq8+7SdyeJW80k2 i8V35ByYPX4tWMrq0XNyHpPHle+rGQOYo7hsUlJzMstSi/TtErgy5px6y1awTbLi3YutjA2M baJdjJwcEgImElO7HrB2MXJxCAkcZZRYeOkmM4TzjVFi64J7zCBVQgIXGSU2fi+GSFxmlFh3 eRo7SIJNwFNi8rtuFhBbREBIYunHy2BxZoEGoFFbOUBsYQF/ieNNSxlBbBYBVYkPG88ArePg 4BVwkrh1WgXiCnmJ1RsOgO3iFHCWOPByASPE3gqJd3+/g43kFRCUODnzCQvEeE2J1u2/oVbJ SzRvnQ11p5bE/SVfmCcwCs1C0jILScssJC0LGJlXMYoWpxYn5aYbGemlFmUmFxfn5+nlpZZs YgSG9sEtvw12ML587niIUYCDUYmHV8v5QIwQa2JZcWXuIUYJDmYlEV6T7ftjhHhTEiurUovy 44tKc1KLDzFKc7AoifNGr94TIySQnliSmp2aWpBaBJNl4uCUamAMF0rXS2qW5RfJF9ojVHfP fJ5y1td54nmWDEt8Rdjsw76d4uieuva6SsCJa1fjzy7amGl+97jbQYXNZ1KeBU/wrfiSsHLX LfYpMnH/5okXidy+eU9w8vIkufjmEtf3d5k2LlTIXbWCaRuHzYbwL/2n/gdmZh1bLpQYZPP0 79LTaXM2bV5S5xenxFKckWioxVxUnAgAzvtOL2kCAAA= Subject: [dpdk-dev] [RFC v3 2/2] eal: introduce random generator function with upper bound X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Message-ID: <20190424123320.RSoddH966shhdQmsvoDPxayvXewlihsvuTS79vPoIWQ@z> 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 --- lib/librte_eal/common/include/rte_random.h | 16 +++++++++ lib/librte_eal/common/rte_random.c | 39 ++++++++++++++++++++++ lib/librte_eal/rte_eal_version.map | 1 + 3 files changed, 56 insertions(+) diff --git a/lib/librte_eal/common/include/rte_random.h b/lib/librte_eal/common/include/rte_random.h index 66dfe8ae7..cd29f3249 100644 --- a/lib/librte_eal/common/include/rte_random.h +++ b/lib/librte_eal/common/include/rte_random.h @@ -47,6 +47,22 @@ 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_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 85dfd0cde..03a186337 100644 --- a/lib/librte_eal/common/rte_random.c +++ b/lib/librte_eal/common/rte_random.c @@ -131,6 +131,45 @@ 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) { rte_srand(rte_get_timer_cycles()); diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map index 381351749..1d3a54021 100644 --- a/lib/librte_eal/rte_eal_version.map +++ b/lib/librte_eal/rte_eal_version.map @@ -376,6 +376,7 @@ 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