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Gianfar used to enable all 8 Rx queues (DMA rings) per ethernet device, even though the controller can only support 2 interrupt lines at most. This meant that multiple Rx queues would have to be grouped per NAPI poll routine, and the CPU would have to split the budget and service them in a round robin manner. The overhead of this scheme proved to outweight the potential benefits. The alternative was to introduce the "Single Queue" polling mode, supporting one Rx queue per NAPI, which became the default packet processing option and helped improve the performance of the driver. MQ_POLLING also relies on undocumeted device tree properties to specify how to map the 8 Rx and Tx queues to a given interrupt line (aka "interrupt group"). Using module parameters to enable this mode wasn't an option either. Long story short, MQ_POLLING became obsolete, now it is just dead code, and no one asked for it so far. For the Tx queues, multi-queue support (more than 1 Tx queue per CPU) could be revisited by adding tc MQPRIO support, but again, one has to consider that there are only 2 interrupt lines. So the NAPI poll routine would have to service multiple Tx rings. Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.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.