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A driver may use build_skb() for received packets. These SKBs then have a head_frag. Since commitd7e8883cfc("net: make GRO aware of skb->head_frag"), GRO may build frag_list SKBs out of head_frag received SKBs. In such a case, the chained SKBs end up with a head_frag. Commit07b26c9454("gso: Support partial splitting at the frag_list pointer") adds partial segmentation of frag_list SKB chains into individual SKBs. However, this is not done if the chained SKBs have any linear part, because the device may not be able to DMA the private linear buffer. A chained frag_list SKB with head_frag is wrongfully detected in this case as having a private linear part and thus falls back to software GSO, while in fact the linear part is backed by a DMA page just like any other frag. This causes low performance when forwarding those packets that were built with build_skb() Allow partial segmentation at the frag_list pointer for chained SKBs with head_frag. Note that such SKBs can only be created by GRO, when applied to received packets with head_frag. Also note that this change only affects the data path that performs the partial segmentation at frag_list pointer, and not any of the other more common data paths. Signed-off-by: Ilan Tayari <ilant@mellanox.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.