9e2bc267e7
This driver was using the TX IRQ handler to perform all TX completion tasks. Under heavy TX network load, this can cause significant irqs-off latencies (found to be in the hundreds of microseconds using ftrace). This can cause other issues, such as overrunning serial UART FIFOs when using high baud rates with limited UART FIFO sizes. Switch to using a NAPI poll handler to perform the TX completion work to get this out of hard IRQ context and avoid the IRQ latency impact. A separate poll handler is used for TX and RX since they have separate IRQs on this controller, so that the completion work for each of them stays on the same CPU as the interrupt. Testing on a Xilinx MPSoC ZU9EG platform using iperf3 from a Linux PC through a switch at 1G link speed showed no significant change in TX or RX throughput, with approximately 941 Mbps before and after. Hard IRQ time in the TX throughput test was significantly reduced from 12% to below 1% on the CPU handling TX interrupts, with total hard+soft IRQ CPU usage dropping from about 56% down to 48%. Signed-off-by: Robert Hancock <robert.hancock@calian.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.