From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 505FFC00140 for ; Sun, 21 Aug 2022 06:20:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=8oGZokvBAgAmGa/AGNYft6cu4JzaUDWu8P4wWm4ppeE=; b=zEmXKUQ+WI6VrdmVqjKbuWXIDk xLogJ2zAFcTUgX9/jVnmF6OoZkYNNr6vGGSXiJKL2yvlCXRYp8uwYp+JOGe2E9M/UKZt427k4XFS4 eVdHBlDZ/Mlr/oXzDqjRRyXqz+ds8lbIdlZBrtLMo/9JjeZ4OiDYAL7QMRAI9fjv9JXLRyMNviMZk yiZmq/rNA/ETGszl5TXuAiE+rJ8HkrflRhw6K/jSNYpLnWS2X44hX/UA88zhUj4ibqszGZRcPtISD XlmzywGPZI/GwLWMVEN6cMADRdjmW2Q5nqMK9ibgqxu/sIk0l8H2759Tm24oLTJ6MBhL53HTg1c/e j/qfAdzw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oPeJt-006heM-Dk; Sun, 21 Aug 2022 06:20:25 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oPeJp-006hcK-SA for linux-nvme@lists.infradead.org; Sun, 21 Aug 2022 06:20:23 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 65E4168C7B; Sun, 21 Aug 2022 08:20:17 +0200 (CEST) Date: Sun, 21 Aug 2022 08:20:16 +0200 From: Christoph Hellwig To: Chao Leng Cc: linux-nvme@lists.infradead.org, hch@lst.de, sagi@grimberg.me, kbusch@kernel.org Subject: Re: [PATCH] nvme-rdma: set ack timeout of RoCE to 262ms Message-ID: <20220821062016.GA26553@lst.de> References: <20220819075825.21231-1-lengchao@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220819075825.21231-1-lengchao@huawei.com> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220820_232022_115838_CD6A4783 X-CRM114-Status: GOOD ( 12.89 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Fri, Aug 19, 2022 at 03:58:25PM +0800, Chao Leng wrote: > Now the ack timeout of RoCE is 2 second(2^(18+1)*4us=2 second). In the > case of low concurrency, if some packets lost due to network abnormal > such as network rerouting, Optical fiber signal interference, etc, > it will wait 2 second to try retransmitting the lost packets. > As a result, the I/O latency is greater than 2 seconds. > The I/O latency is so long for real-time transaction service. Indeed we > do not have to wait so long time to make sure that packets are lost. > Setting the ack timeout to 262ms(2^(15+1)*4us=262ms) is sufficient. I'll leave people more familar with RoCE to judge the merits of this change, but I really want a comment explaining the choice in the source code.