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0dc9324206
To make hardware efficient to determine if RX ring is full, introduce new
design that checks if reading and writing indices are equal. Comparing
to old design, initial indices of both reading and writing indices are 0
that means empty, and hardware checks full by "writing index + 1 ==
reading index". The "+1" has extra cost for hardware, so new design is
to avoid this.
Take ring size is 256 as an example, the initial reading and writing
indices are 255 and 0 respectively; the initial values mean empty. If two
indices are the same, for example 5 and 5, it means ring is full.
wp rp used_cnt state
255 0 0 initial (ring is empty)
255 1 1 receive 1st packet
255 2 2 receive 2nd packet
0 2 1 driver read 1st packet
1 2 0 driver read 2nd packet (ring is empty)
:
5 5 255 ring is full
Note: 'rp' is hardware writing index
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231026120049.9187-4-pkshih@realtek.com
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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.