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 17D8FCA9ED1 for ; Mon, 12 Oct 2026 14:39:51 +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:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=xP1oht89CwRZ8lK8dc2psCTyCsXfeaCRWjUSkyJhkJg=; b=JltuslqV7AWi8nYuUZH7biLXMm QcT8j7sxwxMOOFVU848ebF/u6rfYuDmNLNxZxt41eViFUUMzKmbqxGeQ/n8qsRQcKbWTypB2oFszF FpLi/85JqT8kUmCM2awCIy3KFGTMbyNW3YAPoz933k2wCIx1/ftcBGH70OtVGs/EsU1+aG+OhlTPi 9iTMPgHro0lTHl0r6rkiIWIRbUSUOkbqC5k6cba3Aio+ldOWE3eJpOAaPMnS+5bE5n7ZcCzzjA5uG xQgYLknPKj/OToQm9NJwqKU55pYZUKWMfmP07+ilNQr/DZutc61tx+KKZBTuSfh6XtTW6CsF6BdGp kSs6v4Gg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGHBs-0000000AhzJ-3MDs; Mon, 12 Oct 2026 14:39:48 +0000 Received: from out-179.mta1.migadu.com ([2001:41d0:203:375::b3] helo=mta1.migadu.com) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGHBn-0000000Ahyh-0isL for linux-nvme@lists.infradead.org; Mon, 12 Oct 2026 14:39:44 +0000 X-Envelope-To: linux-nvme@lists.infradead.org DKIM-Signature: a=rsa-sha256; bh=CEkn6V5ALhhqhhpxb3OWlxXupE8t6sIgFZ0BVdRWG90=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791815981; v=1; x=1792420781; b=mdCytkoSLrzPBrXSb6TPfgPUphJ/NUPDhEGvUnJTGA/XcBrDJm0n63PNRkBO0F/mT7DKCquG 6P23U0b7lVFP6pP3ojn+9oIwDXFGeV9g1KgUAC8ewe92sduxyrwgxym0wN1hVWR7zsEOF74aFEs QnRiTRqgZRagLLfXqU9/Ya9A= X-Envelope-To: linux-nvme@lists.infradead.org Received: by mta12.migadu.com with ESMTPS id c71f62ae9e69f9bb; Mon, 12 Oct 2026 14:39:41 +0000 X-Mizu-Trace-ID: c71f62ae9e69f9bb X-Migadu-Flow: FLOW_OUT Message-ID: <8894307f-1042-497c-9c16-3fc1312486fb@linux.dev> Date: Mon, 12 Oct 2026 15:39:36 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [External] Re: [PATCH] Revert "nvme-pci: clamp max_hw_sectors based on DMA optimized limitation" To: Christoph Hellwig Cc: Adrian Huang12 , "kbusch@kernel.org" , "sagi@grimberg.me" , "linux-nvme@lists.infradead.org" , Jiwei JW10 Sun , "iommu@lists.linux.dev" References: <20261006120248.147654-1-hch@lst.de> <8cf8a8ea-c9c9-434b-aec6-e361280a88a4@linux.dev> <20261008123724.GA22096@lst.de> <2007f03b-2c76-4c36-a0bd-0ce99d1a01a2@linux.dev> <20261012121736.GE29954@lst.de> Content-Language: en-US From: John Garry In-Reply-To: <20261012121736.GE29954@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261012_073943_434653_15DC3CF1 X-CRM114-Status: GOOD ( 14.68 ) 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 10/12/26 13:17, Christoph Hellwig wrote: > On Mon, Oct 12, 2026 at 09:42:04AM +0100, John Garry wrote: >> And now we seem to have a conflict, as Christoph wants block size > IOVA >> rcache limit but you find it may cause this soft lockup. >> >>> 2. Another NVME with mdts=5 (maximum data transfer size = 128KB) >>> 2.1 The issue does not reproduce regardless of the 'bs' configuration >>> 3. The condition '128 KB' is identified because the IOMMU scalable IOVA mechanism supports a maximum transfer size of 128 KB. >>> 4. IOMMU pass-through mode does not trigger the issue with the 'mdts=10' nvme disk. >>> 5. The issue only appears with high-core-count servers >>> 5.1 Reproduced servers: 448-core server and 384-core server >>> 5.2 Non-reproduced server: 128-core server >> >> How long does it take for the lockup to trigger? Pretty quickly, I guess. >> >> Does changing the number of CPUs affect throughput (before the lockup)? Are >> you using just a single disk? > > If the iova cache locks up under a perfectly normal workloads it > is broken. > We really need to fix the code there. Sure, but it would help to first fully understand the conditions to fix it.