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dccce1d7c0
The tsnep network controller is able to extend the descriptor directly with data to be transmitted. In this case no TX data DMA address is necessary. Instead of the TX data DMA address the TX data buffer is placed at the end of the descriptor. The descriptor is read with a 64 bytes DMA read by the tsnep network controller. If the sum of descriptor data and TX data is less than or equal to 64 bytes, then no additional DMA read is necessary to read the TX data. Therefore, it makes sense to inline small fragments up to this limit within the descriptor ring. Inlined fragments need to be copied to the descriptor ring. On the other hand DMA mapping is not necessary. At most 40 bytes are copied, so copying should be faster than DMA mapping. For A53 1.2 GHz copying takes <100ns and DMA mapping takes >200ns. So inlining small fragments should result in lower CPU load. Performance improvement is small. Thus, comparision of CPU load with and without inlining of small fragments did not show any significant difference. With this optimization less DMA reads will be done, which decreases the load of the interconnect. Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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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.