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{ "id": 839, "url": "http://patchwork.dpdk.org/api/covers/839/?format=api", "web_url": "http://patchwork.dpdk.org/project/dpdk/cover/1712250913-1977-1-git-send-email-roretzla@linux.microsoft.com/", "project": { "id": 1, "url": "http://patchwork.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": "<1712250913-1977-1-git-send-email-roretzla@linux.microsoft.com>", "list_archive_url": "https://inbox.dpdk.org/dev/1712250913-1977-1-git-send-email-roretzla@linux.microsoft.com", "date": "2024-04-04T17:15:09", "name": "[0/4] RFC samples converting VLA to alloca", "submitter": { "id": 2077, "url": "http://patchwork.dpdk.org/api/people/2077/?format=api", "name": "Tyler Retzlaff", "email": "roretzla@linux.microsoft.com" }, "mbox": "http://patchwork.dpdk.org/project/dpdk/cover/1712250913-1977-1-git-send-email-roretzla@linux.microsoft.com/mbox/", "series": [ { "id": 31680, "url": "http://patchwork.dpdk.org/api/series/31680/?format=api", "web_url": "http://patchwork.dpdk.org/project/dpdk/list/?series=31680", "date": "2024-04-04T17:15:09", "name": "RFC samples converting VLA to alloca", "version": 1, "mbox": "http://patchwork.dpdk.org/series/31680/mbox/" } ], "comments": "http://patchwork.dpdk.org/api/covers/839/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 9E5E543DFB;\n\tThu, 4 Apr 2024 19:15:17 +0200 (CEST)", "from mails.dpdk.org (localhost [127.0.0.1])\n\tby mails.dpdk.org (Postfix) with ESMTP id 1A90B402E8;\n\tThu, 4 Apr 2024 19:15:17 +0200 (CEST)", "from linux.microsoft.com (linux.microsoft.com [13.77.154.182])\n by mails.dpdk.org (Postfix) with ESMTP id 03D5A402E8\n for <dev@dpdk.org>; Thu, 4 Apr 2024 19:15:15 +0200 (CEST)", "by linux.microsoft.com (Postfix, from userid 1086)\n id 3AC8320E94A3; Thu, 4 Apr 2024 10:15:14 -0700 (PDT)" ], "DKIM-Filter": "OpenDKIM Filter v2.11.0 linux.microsoft.com 3AC8320E94A3", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com;\n s=default; t=1712250914;\n bh=APOPtIYhw2AUB6f6nOwZ/x3WKAr4J1YZm8yELcFMKgA=;\n h=From:To:Cc:Subject:Date:In-Reply-To:References:From;\n b=dc/7oxQNU7BEgWpFZaAumJ8LvpuvB4a5QndNsatf41B/Gwidqs0QE7/Wmc92eOwnR\n lz22ezp67VvnjASGTL6Bwpf1lSh1Rb4Qm54nHn40oGhmnXit1nJ5duN55vFhWqWvmK\n Jwogv8eY1B++Ad1J53CMAWkBZDdIuhuggpUkjJr4=", "From": "Tyler Retzlaff <roretzla@linux.microsoft.com>", "To": "dev@dpdk.org", "Cc": "Bruce Richardson <bruce.richardson@intel.com>,\n Stephen Hemminger <stephen@networkplumber.org>,\n Thomas Monjalon <thomas@monjalon.net>,\n =?utf-8?q?Morten_Br=C3=B8rup?= <mb@smartsharesystems.com>,\n Tyler Retzlaff <roretzla@linux.microsoft.com>", "Subject": "[PATCH 0/4] RFC samples converting VLA to alloca", "Date": "Thu, 4 Apr 2024 10:15:09 -0700", "Message-Id": "<1712250913-1977-1-git-send-email-roretzla@linux.microsoft.com>", "X-Mailer": "git-send-email 1.8.3.1", "In-Reply-To": "\n <20231107193220.GA15232@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>", "References": "\n <20231107193220.GA15232@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>", "X-BeenThere": "dev@dpdk.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "DPDK patches and discussions <dev.dpdk.org>", "List-Unsubscribe": "<https://mails.dpdk.org/options/dev>,\n <mailto:dev-request@dpdk.org?subject=unsubscribe>", "List-Archive": "<http://mails.dpdk.org/archives/dev/>", "List-Post": "<mailto:dev@dpdk.org>", "List-Help": "<mailto:dev-request@dpdk.org?subject=help>", "List-Subscribe": "<https://mails.dpdk.org/listinfo/dev>,\n <mailto:dev-request@dpdk.org?subject=subscribe>", "Errors-To": "dev-bounces@dpdk.org" }, "content": "This series is not intended for merge. It insteat provides examples of\nconverting use of VLAs to alloca() would look like.\n\nwhat's the advantages of VLA over alloca()?\n\n* sizeof(array) works as expected.\n\n* multi-dimensional arrays are still arrays instead of pointers to\n dynamically allocated space. this means multiple subscript syntax\n works (unlike on a pointer) and calculation of addresses into allocated\n space in ascending order is performed by the compiler instead of manually.\n\nwhat's the disadvantage of VLA over alloca()?\n\n* VLA generation is subtl/implicit, there do appear to be places where\n a VLA is being used where it perhaps was not intended but it is hard\n to spot. e.g. hotpath rte_mbuf *array[burst_size]; where burst_size\n is not a constant expression, e.g. unintended in other syntax positions\n that are not intuitive, see patchwork link.\n\n https://patchwork.dpdk.org/project/dpdk/patch/1699896038-28106-1-git-send-email-roretzla@linux.microsoft.com/\n\nfor the above reasons i'd recommend only converting to alloca() where\nnecessary (msvc has to compile it) and for the other instances leave\nthem as they are.\n\nTyler Retzlaff (4):\n latencystats: use alloca instead of vla trivial\n hash: use alloca instead of vla trivial\n vhost: use alloca instead of vla sizeof\n dispatcher: use alloca instead of vla multi dimensional\n\n lib/dispatcher/rte_dispatcher.c | 6 +++---\n lib/hash/rte_thash.c | 2 +-\n lib/latencystats/rte_latencystats.c | 2 +-\n lib/vhost/socket.c | 5 +++--\n 4 files changed, 8 insertions(+), 7 deletions(-)" }