From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC31D47ACD6 for ; Mon, 12 Oct 2026 12:17:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791807465; cv=none; b=d83WFD+OK/Qi/a2UDT5byhgqnnzFZ7A/qgYWwPmWMSQcP1BCKUlukouLfAsa3jRvt7rHP5sAlhGv8x2n3wvlvOrXpWwFQt6HKyDaahQYeMOErYwGPrVHEFEpOPaAWvSn4S0dqULxvwYlMPZjOHgtKFBPgKIPNpFV9mHDA5nNJnw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791807465; c=relaxed/simple; bh=a97eitSQlYdigcawlcd8+/c0hBgHCxsubwLctE3uf8c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=N8rI7p9Axdkm68s19k0HbS09U+wxWDmUXx1fzYEJ1dF9au6xttT4nstadfrlh4BqFCVI+i2uyPDzZt5W0SRcFPpSV1KUC+LF7o2mkPrMjUt0sVythKo4vXoljmx/hbRcNiruG3+25dS+CSP1fSvmi/73tidIj2Dy7/uUnygk6/s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de 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> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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) 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.