From: Christoph Hellwig <hch@lst.de>
To: Daniel Gomez <da.gomez@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
Keith Busch <kbusch@kernel.org>, Sagi Grimberg <sagi@grimberg.me>,
Chaitanya Kulkarni <kch@nvidia.com>,
Kanchan Joshi <joshi.k@samsung.com>,
Leon Romanovsky <leon@kernel.org>,
Nitesh Shetty <nj.shetty@samsung.com>,
Logan Gunthorpe <logang@deltatee.com>,
linux-block@vger.kernel.org, linux-nvme@lists.infradead.org
Subject: Re: [PATCH 7/9] nvme-pci: convert the data mapping blk_rq_dma_map
Date: Mon, 16 Jun 2025 13:33:55 +0200 [thread overview]
Message-ID: <20250616113355.GA21945@lst.de> (raw)
In-Reply-To: <4af8a37c-68ca-4098-8572-27e4b8b35649@kernel.org>
On Mon, Jun 16, 2025 at 09:41:15AM +0200, Daniel Gomez wrote:
> >> Adding support to
> >> multiple SGL segments should allow us to increase this limit 256 -> 2048.
> >>
> >> Is this correct?
> >
> > Yes. Note that plenty of hardware doesn't really like chained SGLs too
> > much and you might get performance degradation.
> >
>
> I see the driver assumes better performance on SGLs over PRPs when I/Os are
> greater than 32k (this is the default sgl threshold).
Yes. Although that might be worth revisiting - the threshold was we
benchmarked on the first hardware we got hold off that supports SGLs.
> But what if chaining SGL
> is needed, i.e. my host segments are between 4k and 16k, would PRPs perform
> better than chaining SGLs?
Right now we don't support chaining of SGL descriptors, so that's a moot
point.
> Also, if host segments are between 4k and 16k, PRPs would be able to support it
> but this limit prevents that use case. I guess the question is if you see any
> blocker to enable this path?
Well, if you think it's worth it give it a spin on a wide variety of
hardware.
next prev parent reply other threads:[~2025-06-16 12:34 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-10 5:06 new DMA API conversion for nvme-pci Christoph Hellwig
2025-06-10 5:06 ` [PATCH 1/9] block: don't merge different kinds of P2P transfers in a single bio Christoph Hellwig
2025-06-10 12:44 ` Leon Romanovsky
2025-06-10 15:37 ` Keith Busch
2025-06-11 3:43 ` Christoph Hellwig
2025-06-11 16:26 ` Keith Busch
2025-06-11 16:39 ` Logan Gunthorpe
2025-06-11 16:41 ` Keith Busch
2025-06-11 19:41 ` Logan Gunthorpe
2025-06-11 20:00 ` Keith Busch
2025-06-12 4:57 ` Christoph Hellwig
2025-06-12 6:24 ` Kanchan Joshi
2025-06-13 6:19 ` Christoph Hellwig
2025-06-12 15:22 ` Logan Gunthorpe
2025-06-10 5:06 ` [PATCH 2/9] block: add scatterlist-less DMA mapping helpers Christoph Hellwig
2025-06-10 12:51 ` Leon Romanovsky
2025-06-11 13:43 ` Daniel Gomez
2025-06-16 5:02 ` Christoph Hellwig
2025-06-16 6:43 ` Daniel Gomez
2025-06-16 11:31 ` Christoph Hellwig
2025-06-16 12:37 ` Daniel Gomez
2025-06-16 12:42 ` Christoph Hellwig
2025-06-16 12:52 ` Daniel Gomez
2025-06-16 13:01 ` Christoph Hellwig
2025-06-12 6:35 ` Kanchan Joshi
2025-06-13 6:17 ` Christoph Hellwig
2025-06-10 5:06 ` [PATCH 3/9] nvme-pci: simplify nvme_pci_metadata_use_sgls Christoph Hellwig
2025-06-10 12:52 ` Leon Romanovsky
2025-06-11 21:38 ` Keith Busch
2025-06-12 4:59 ` Christoph Hellwig
2025-06-10 5:06 ` [PATCH 4/9] nvme-pci: refactor nvme_pci_use_sgls Christoph Hellwig
2025-06-10 13:10 ` Leon Romanovsky
2025-06-11 13:43 ` Daniel Gomez
2025-06-12 5:00 ` Christoph Hellwig
2025-06-11 20:50 ` Keith Busch
2025-06-12 5:00 ` Christoph Hellwig
2025-06-10 5:06 ` [PATCH 5/9] nvme-pci: merge the simple PRP and SGL setup into a common helper Christoph Hellwig
2025-06-10 13:13 ` Leon Romanovsky
2025-06-11 13:44 ` Daniel Gomez
2025-06-12 5:01 ` Christoph Hellwig
2025-06-11 21:03 ` Keith Busch
2025-06-12 5:01 ` Christoph Hellwig
2025-06-10 5:06 ` [PATCH 6/9] nvme-pci: remove superfluous arguments Christoph Hellwig
2025-06-10 13:15 ` Leon Romanovsky
2025-06-11 21:05 ` Keith Busch
2025-06-10 5:06 ` [PATCH 7/9] nvme-pci: convert the data mapping blk_rq_dma_map Christoph Hellwig
2025-06-10 13:19 ` Leon Romanovsky
2025-06-11 12:15 ` Daniel Gomez
2025-06-12 5:02 ` Christoph Hellwig
2025-06-16 7:41 ` Daniel Gomez
2025-06-16 11:33 ` Christoph Hellwig [this message]
2025-06-17 17:33 ` Daniel Gomez
2025-06-17 23:25 ` Keith Busch
2025-06-17 17:43 ` Daniel Gomez
2025-06-17 17:45 ` Daniel Gomez
2025-06-11 14:13 ` Daniel Gomez
2025-06-12 5:03 ` Christoph Hellwig
2025-06-16 7:49 ` Daniel Gomez
2025-06-16 11:35 ` Christoph Hellwig
2025-06-10 5:06 ` [PATCH 8/9] nvme-pci: replace NVME_MAX_KB_SZ with NVME_MAX_BYTE Christoph Hellwig
2025-06-10 13:20 ` Leon Romanovsky
2025-06-11 14:00 ` Daniel Gomez
2025-06-10 5:06 ` [PATCH 9/9] nvme-pci: rework the build time assert for NVME_MAX_NR_DESCRIPTORS Christoph Hellwig
2025-06-10 13:21 ` Leon Romanovsky
2025-06-11 13:51 ` Daniel Gomez
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