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Thu, 19 Mar 2026 09:40:53 +0000 Date: Thu, 19 Mar 2026 09:40:48 +0000 From: Bruce Richardson To: Morten =?iso-8859-1?Q?Br=F8rup?= CC: , Andrew Rybchenko Subject: Re: [PATCH] doc: remove obsolete mempool creation advice Message-ID: References: <20260319091300.652853-1-mb@smartsharesystems.com> Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260319091300.652853-1-mb@smartsharesystems.com> X-ClientProxiedBy: DU6P191CA0039.EURP191.PROD.OUTLOOK.COM (2603:10a6:10:53f::13) To DS0PR11MB7309.namprd11.prod.outlook.com (2603:10b6:8:13e::17) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7309:EE_|BL1PR11MB5317:EE_ X-MS-Office365-Filtering-Correlation-Id: 761e1055-402d-4fb0-5a2a-08de859b9cbe X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; ARA:13230040|366016|1800799024|376014|18002099003|22082099003|56012099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255; 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If passing a power-of-2 size to mempool create one will get a backing rte_ring store which is twice as large as requested, leading to lots of ring slots being wasted. For example, for a pool with 16k elements, the actual ring size allocated will be 32k, leading to wasting 128k of RAM, and also potentially cache too. The latter will occur because of the nature of the ring to iterate through all mempool/ring entries, meaning that even if only 16k of the 32k slots will ever be used, all 32k slots will be passed through the cpu cache if it works on the mempool directly and not just from the per-core cache. On the other hand, I'd be in favour of removing this text if we switched the default mempool in DPDK to being stack-based. While the stack may not be lock-free like the ring, with per-lcore caches the number of accesses to the stack should be small, and it gives much better cache utilization overall - especially in cases where buffers are allocated on one core and freed on a different one! Even in cases where we are not transferring between cores, in a single-core case we still will get better reuse of "hot" buffers than in an rte_ring-backed case. /Bruce