From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-203.mta0.migadu.com [91.218.175.203]) (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 A4769439F75 for ; Thu, 15 Oct 2026 10:30:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.203 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792060259; cv=none; b=tkhDxLiC3oxcibbKOWgsZKWFFO8KlYCWMhO6USZKqofLvxFDAa0rJNtFWaimMvAcmh0o1Ego5tswGZWWJWQ1MFbMwV76f8m89cZOtsvYSQLox6DKtm6N5ZmOuuKQPxxqNDDzgtgBOQpwrZpTGz7kl4dneb58V//9CtaPtafnWc4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792060259; c=relaxed/simple; bh=KL50O/iWsTHmbo6NadhTpGohH+0IwIFZqJc3pja8taE=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=DlIvn4fOH3euMt1bj1uyJwmfofP9cfIKs+Iz/NauhIBquUXadxRqYGQQFXl+DPo+lCmlGm/9uOgxOOTXqv8Wl2HpwsZzFBaJGnxMi4eDPgrMy8ibUYM9B62gvAnhmHmVt4e3Zq05oQL26lvPBBiS8O1IyonuLmwoqLn8iF805wg= 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=LQtHygRS; arc=none smtp.client-ip=91.218.175.203 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="LQtHygRS" X-Envelope-To: iommu@lists.linux.dev DKIM-Signature: a=rsa-sha256; bh=KL50O/iWsTHmbo6NadhTpGohH+0IwIFZqJc3pja8taE=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1792060255; v=1; x=1792665055; b=LQtHygRSVbiX/tqocinrRwPZYKTkWTJ6aD/vJe6ehxQdft2TFWZSueOOBh6MnqHfRQGag1DN W6GoQGbL6WXpUxmnNbYEgm10kkLtPeTQ4nbjdTfxoQXIc0kL5xKvlgpMOo1S7uXDL3p4L/zGCtn 8rddGaTkUafnq9OoGKhpzv2M= X-Envelope-To: iommu@lists.linux.dev Received: by mta11.migadu.com with ESMTPS id dd78c0c2979e365e; Thu, 15 Oct 2026 10:30:55 +0000 X-Mizu-Trace-ID: dd78c0c2979e365e X-Migadu-Flow: FLOW_OUT Message-ID: Date: Thu, 15 Oct 2026 11:30:49 +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" From: John Garry To: Christoph Hellwig , Adrian Huang12 Cc: "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> <8894307f-1042-497c-9c16-3fc1312486fb@linux.dev> Content-Language: en-US In-Reply-To: <8894307f-1042-497c-9c16-3fc1312486fb@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/12/26 15:39, John Garry wrote: > 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. BTW, @Adrian, it would be good to run your test with the IOMMU in strict mode as well, just to give an idea if there is a problem there as well.