From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9577748EC68 for ; Mon, 12 Oct 2026 14:39:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791815986; cv=none; b=UNeJ41KCm7PdTHNjHeuPgh4aDHjNJzemHUKUXepBvFtqiigIcpICaeP46HSm8ZmA/N6D/y/CXIHoiYb6WR78UCxQz2kl9AmWwtswarftb1qAm9WdAgJ+mXmb09ivbSR8fsv4t7BIJyCpUVmrAbVumP/vKncM1REXoKqhn311R6c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791815986; c=relaxed/simple; bh=CEkn6V5ALhhqhhpxb3OWlxXupE8t6sIgFZ0BVdRWG90=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZfQmVOdxTeYwgl9mpLwoQiquDVwsyozS1hmcBen8vb0kqvfr2mM64oOMbcA++QmIEibHb44R0ALysUTpsPjDs+Ur6t+xGK1ZLFOkfZih24eQ0XFHypANcoJt2Y9ug4iinS14SKeSynWsT04fiMBvYABrVCu32URmejRD7j+6GT4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=mdCytkoS; arc=none smtp.client-ip=91.218.175.184 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="mdCytkoS" X-Envelope-To: iommu@lists.linux.dev 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: iommu@lists.linux.dev 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 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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 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.