From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.garry@linux.dev>
Cc: Adrian Huang12 <ahuang12@lenovo.com>,
Christoph Hellwig <hch@lst.de>,
"kbusch@kernel.org" <kbusch@kernel.org>,
"sagi@grimberg.me" <sagi@grimberg.me>,
"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
Jiwei JW10 Sun <sunjw10@lenovo.com>,
"iommu@lists.linux.dev" <iommu@lists.linux.dev>
Subject: Re: [External] Re: [PATCH] Revert "nvme-pci: clamp max_hw_sectors based on DMA optimized limitation"
Date: Mon, 12 Oct 2026 14:17:36 +0200 [thread overview]
Message-ID: <20261012121736.GE29954@lst.de> (raw)
In-Reply-To: <2007f03b-2c76-4c36-a0bd-0ce99d1a01a2@linux.dev>
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.
next prev parent reply other threads:[~2026-10-12 12:18 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-06 12:02 [PATCH] Revert "nvme-pci: clamp max_hw_sectors based on DMA optimized limitation" Christoph Hellwig
2026-10-08 7:36 ` John Garry
2026-10-08 12:37 ` Christoph Hellwig
2026-10-09 9:11 ` [External] " Adrian Huang12
2026-10-09 15:37 ` Keith Busch
2026-10-12 8:42 ` John Garry
2026-10-12 12:17 ` Christoph Hellwig [this message]
2026-10-12 14:39 ` John Garry
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