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Mon, 16 Mar 2026 14:02:27 -0700 (PDT) Received: from localhost ([2a03:2880:2ff:71::]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82a072422desm14800519b3a.1.2026.03.16.14.02.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Mar 2026 14:02:27 -0700 (PDT) Date: Mon, 16 Mar 2026 14:02:26 -0700 From: Joe Damato To: Leon Romanovsky Cc: netdev@vger.kernel.org, michael.chan@broadcom.com, pavan.chebbi@broadcom.com, linux-kernel@vger.kernel.org, Marek Szyprowski Subject: Re: [RFC net-next v2 00/12] Add TSO map-once DMA helpers and bnxt SW USO support Message-ID: Mail-Followup-To: Joe Damato , Leon Romanovsky , netdev@vger.kernel.org, michael.chan@broadcom.com, pavan.chebbi@broadcom.com, linux-kernel@vger.kernel.org, Marek Szyprowski References: <20260312223457.1999489-1-joe@dama.to> <20260316194419.GH61385@unreal> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260316194419.GH61385@unreal> On Mon, Mar 16, 2026 at 09:44:19PM +0200, Leon Romanovsky wrote: > On Thu, Mar 12, 2026 at 03:34:37PM -0700, Joe Damato wrote: > > Greetings: > > > > This series extends net/tso to add a data structure and some helpers allowing > > drivers to DMA map headers and packet payloads a single time. The helpers can > > then be used to reference slices of shared mapping for each segment. This > > helps to avoid the cost of repeated DMA mappings, especially on systems which > > use an IOMMU. > > In modern kernels, it is done by using DMA IOVA API, see NVMe > driver/block layer for the most comprehensive example. > > The pseudo code is: > if (with_iommu) > use dma_iova_link/dma_iova_unlink > else > use dma_map_phys() > > https://lore.kernel.org/all/cover.1746424934.git.leon@kernel.org/ > https://lore.kernel.org/all/20250623141259.76767-1-hch@lst.de/ > https://lwn.net/Articles/997563/ Thanks for the pointer. I agree it's the right approach. Batching the IOVA allocation and IOTLB sync across all regions is a clear win over the per-region dma_map_single/skb_frag_dma_map calls I had in v2. I'll submit a v3 with the tso_dma_map internals updated to use dma_iova_try_alloc + dma_iova_link + dma_iova_sync, with a dma_map_phys fallback.