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 133D0CA9ED1 for ; Mon, 12 Oct 2026 12:18:05 +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=7DZ29KSR5IQVfS14SvRysgyJyIe/qfWk7fwLE+3d+MI=; b=PPu5no0ne9gVYsp8WQhA86QSmo OeGAf1i5bqmn4xp8JRb2bQweNbFIxw5AjIoXPB7dDznOPPuWWUM+MngaBX7DuNkb6QTgPoUSevo2S rvblUZLcFq/BegGVP6LSQmuDZWQ13HhRmILHEmjphBIdJF+EOXNyvjAkhkDifMjokbCW80bf4mYiM 6JYfOqp639a7F3ZNAWVl9PuMlXLGLcXRlKE36lPnCilMGLIEA/7S0y/+3EXJn12oe/kuXEKnVVZBc YDv6u0OsK5UCC87i/7JXS/XeImKO5IDJjol8GwbdTHt7x+/H1gPAOC/d+XEIejvjujOHuw7dEgb4N asV1/TUw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGEyg-0000000AQk4-3TOV; Mon, 12 Oct 2026 12:18:02 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGEyT-0000000AQNB-3hdx for linux-nvme@lists.infradead.org; Mon, 12 Oct 2026 12:17:51 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 5D7F96732A; Mon, 12 Oct 2026 14:17:37 +0200 (CEST) Date: Mon, 12 Oct 2026 14:17:36 +0200 From: Christoph Hellwig To: John Garry Cc: Adrian Huang12 , Christoph Hellwig , "kbusch@kernel.org" , "sagi@grimberg.me" , "linux-nvme@lists.infradead.org" , Jiwei JW10 Sun , "iommu@lists.linux.dev" Subject: Re: [External] Re: [PATCH] Revert "nvme-pci: clamp max_hw_sectors based on DMA optimized limitation" Message-ID: <20261012121736.GE29954@lst.de> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2007f03b-2c76-4c36-a0bd-0ce99d1a01a2@linux.dev> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261012_051750_075514_5BF495EE X-CRM114-Status: GOOD ( 16.24 ) 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 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.