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The LAN743x/PCI11xxx DMA descriptors are always 4 dwords long, but the device supports placing the descriptors in memory back to back or reserving space in between them using its DMA_DESCRIPTOR_SPACE (DSPACE) configurable hardware setting. Currently DSPACE is unnecessarily set to match the host's L1 cache line size, resulting in space reserved in between descriptors in most platforms and causing a suboptimal behavior (single PCIe Mem transaction per descriptor). By changing the setting to DSPACE=16 many descriptors can be packed in a single PCIe Mem transaction resulting in a massive performance improvement in bidirectional tests without any negative effects. Tested and verified improvements on x64 PC and several ARM platforms (typical data below) Test setup 1: x64 PC with LAN7430 ---> x64 PC iperf3 UDP bidirectional with DSPACE set to L1 CACHE Size: - - - - - - - - - - - - - - - - - - - - - - - - - [ ID][Role] Interval Transfer Bitrate [ 5][TX-C] 0.00-10.00 sec 170 MBytes 143 Mbits/sec sender [ 5][TX-C] 0.00-10.04 sec 169 MBytes 141 Mbits/sec receiver [ 7][RX-C] 0.00-10.00 sec 1.02 GBytes 876 Mbits/sec sender [ 7][RX-C] 0.00-10.04 sec 1.02 GBytes 870 Mbits/sec receiver iperf3 UDP bidirectional with DSPACE set to 16 Bytes - - - - - - - - - - - - - - - - - - - - - - - - - [ ID][Role] Interval Transfer Bitrate [ 5][TX-C] 0.00-10.00 sec 1.11 GBytes 956 Mbits/sec sender [ 5][TX-C] 0.00-10.04 sec 1.11 GBytes 951 Mbits/sec receiver [ 7][RX-C] 0.00-10.00 sec 1.10 GBytes 948 Mbits/sec sender [ 7][RX-C] 0.00-10.04 sec 1.10 GBytes 942 Mbits/sec receiver Test setup 2 : RK3399 with LAN7430 ---> x64 PC RK3399 Spec: The SOM-RK3399 is ARM module designed and developed by FriendlyElec. Cores: 64-bit Dual Core Cortex-A72 + Quad Core Cortex-A53 Frequency: Cortex-A72(up to 2.0GHz), Cortex-A53(up to 1.5GHz) PCIe: PCIe x4, compatible with PCIe 2.1, Dual operation mode iperf3 UDP bidirectional with DSPACE set to L1 CACHE Size: - - - - - - - - - - - - - - - - - - - - - - - - - [ ID][Role] Interval Transfer Bitrate [ 5][TX-C] 0.00-10.00 sec 534 MBytes 448 Mbits/sec sender [ 5][TX-C] 0.00-10.05 sec 534 MBytes 446 Mbits/sec receiver [ 7][RX-C] 0.00-10.00 sec 1.12 GBytes 961 Mbits/sec sender [ 7][RX-C] 0.00-10.05 sec 1.11 GBytes 946 Mbits/sec receiver iperf3 UDP bidirectional with DSPACE set to 16 Bytes - - - - - - - - - - - - - - - - - - - - - - - - - [ ID][Role] Interval Transfer Bitrate [ 5][TX-C] 0.00-10.00 sec 966 MBytes 810 Mbits/sec sender [ 5][TX-C] 0.00-10.04 sec 965 MBytes 806 Mbits/sec receiver [ 7][RX-C] 0.00-10.00 sec 1.11 GBytes 956 Mbits/sec sender [ 7][RX-C] 0.00-10.04 sec 1.07 GBytes 919 Mbits/sec receiver Signed-off-by: Vishvambar Panth S <vishvambarpanth.s@microchip.com> Reviewed-by: Simon Horman <horms@kernel.org> Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com> Link: https://lore.kernel.org/r/20231116054350.620420-1-vishvambarpanth.s@microchip.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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.