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{ "id": 122072, "url": "https://patches.dpdk.org/api/covers/122072/?format=api", "web_url": "https://patches.dpdk.org/project/dpdk/cover/1673615325-20624-1-git-send-email-vipinp@vmware.com/", "project": { "id": 1, "url": "https://patches.dpdk.org/api/projects/1/?format=api", "name": "DPDK", "link_name": "dpdk", "list_id": "dev.dpdk.org", "list_email": "dev@dpdk.org", "web_url": "http://core.dpdk.org", "scm_url": "git://dpdk.org/dpdk", "webscm_url": "http://git.dpdk.org/dpdk", "list_archive_url": "https://inbox.dpdk.org/dev", "list_archive_url_format": "https://inbox.dpdk.org/dev/{}", "commit_url_format": "" }, "msgid": "<1673615325-20624-1-git-send-email-vipinp@vmware.com>", "list_archive_url": "https://inbox.dpdk.org/dev/1673615325-20624-1-git-send-email-vipinp@vmware.com", "date": "2023-01-13T13:08:43", "name": "[0/2] *** Memory Allocation: Fixes ms_idx jump in fb_array library ***", "submitter": { "id": 2933, "url": "https://patches.dpdk.org/api/people/2933/?format=api", "name": "Vipin P R", "email": "vipinp@vmware.com" }, "mbox": "https://patches.dpdk.org/project/dpdk/cover/1673615325-20624-1-git-send-email-vipinp@vmware.com/mbox/", "series": [ { "id": 26550, "url": "https://patches.dpdk.org/api/series/26550/?format=api", "web_url": "https://patches.dpdk.org/project/dpdk/list/?series=26550", "date": "2023-01-13T13:08:43", "name": "*** Memory Allocation: Fixes ms_idx jump in fb_array library ***", "version": 1, "mbox": "https://patches.dpdk.org/series/26550/mbox/" } ], "comments": "https://patches.dpdk.org/api/covers/122072/comments/", "headers": { "Return-Path": "<dev-bounces@dpdk.org>", "X-Original-To": "patchwork@inbox.dpdk.org", "Delivered-To": "patchwork@inbox.dpdk.org", "Received": [ "from mails.dpdk.org (mails.dpdk.org [217.70.189.124])\n\tby inbox.dpdk.org (Postfix) with ESMTP id DA556423E6;\n\tSun, 15 Jan 2023 21:11:40 +0100 (CET)", "from mails.dpdk.org (localhost [127.0.0.1])\n\tby mails.dpdk.org (Postfix) with ESMTP id 7D27740156;\n\tSun, 15 Jan 2023 21:11:40 +0100 (CET)", "from CO1PR02CU001-vft-obe.outbound.protection.outlook.com\n (mail-westus2azon11011008.outbound.protection.outlook.com [52.101.47.8])\n by mails.dpdk.org (Postfix) with ESMTP id DDC0140E03\n for <dev@dpdk.org>; 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In legacy mem, allocator assumes that PA contiguous are VA contiguous as well.\n\nReason for the ms_idx going back :\nIn the lookahead logic of find_next_n(), if we fail to find contiguous \"need\" bits, we ignore all masks till the lookahead when we run out of options i.e. the LSB bit is not set or more accurately there are no \"need\" bits starting from LSB, therefore breaking contiguity.\n\nThe optimisation is to avoid repeating this operation and therefore we start from msk_idx = lookahead_idx in the next iter.. However, in the outer loop, we increment msk_idx further, resulting in msk_idx = lookahead_idx + 1, thereby inducing a jump. This problem becomes apparent when we have partially filled bits in the lookahead_msk. Further iterations might find the necessary contiguity from such a lookahead, potentially resulting in the returned ms_idx value to be lower for subsequent iterations.\n\nThe assumption was that ms_idx from rte_fbarray_find_next_n_free() is supposed to be incremental in nature, provided that the value of n is always constant.\n\nFor a sample input of {1, 1070, 1, 2, 1, 2, 4, 12, 2, 2, 1, 2, 1},\n\nWithout the patch :\n\n6358 EAL: ms_idx:1097\n6359 EAL: ms_idx:1098\n6360 EAL: ms_idx:1099\n6361 EAL: ms_idx:1155\n6362 EAL: ms_idx:1156\n6363 EAL: ms_idx:1158\n6364 EAL: ms_idx:1159\n6365 EAL: ms_idx:1154\n6366 EAL: ms_idx:1161\n6367 EAL: ms_idx:1162\n6368 EAL: ms_idx:1164\n\nWith the patch :\n\n12730 EAL: ms_idx:1096\n12731 EAL: ms_idx:1097\n12732 EAL: ms_idx:1098\n12733 EAL: ms_idx:1099\n12734 EAL: ms_idx:1101\n12735 EAL: ms_idx:1102\n12736 EAL: ms_idx:1104\n12737 EAL: ms_idx:1105\n12738 EAL: ms_idx:1107\n12739 EAL: ms_idx:1109\n12740 EAL: ms_idx:1110\n12741 EAL: ms_idx:1112\n\n***\n\nVipin P R (2):\n Memory Allocation: Fixes ms_idx jump (lookahead) during find_next_n()\n in fb_array library\n Memory Allocation: Fixes ms_idx jump (lookbehind) during find_prev_n()\n in fb_array library\n\n .mailmap | 1 +\n lib/eal/common/eal_common_fbarray.c | 4 ++--\n 2 files changed, 3 insertions(+), 2 deletions(-)" }