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Using the queue based tx buffer, it is also possible to allocate a sgl buffer, and use skb_to_sgvec() to convert the skb to the sgvec in order to support the dma_map_sg() to decreases the overhead of IOMMU mapping and unmapping. Firstly, it reduces the number of buffers. For example, a tcp skb may have a 66-byte header and 3 fragments of 4328, 32768, and 28064 bytes. With this patch, dma_map_sg() will combine them into two buffers, 66-bytes header and one 65160-bytes fragment by using IOMMU. Secondly, it reduces the number of dma mapping and unmapping. All the original 4 buffers are mapped only once rather than 4 times. The throughput improves above 10% when running single thread of iperf using TCP when IOMMU is in strict mode. Suggested-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.