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In the current implementation, usbnet uses a fixed tx_qlen of: USB2: 60 * 1518 bytes = 91.08 KB USB3: 60 * 5 * 1518 bytes = 454.80 KB Such large transmit queues can be problematic, especially for cellular modems. For example, with a typical celluar link speed of 10 Mbit/s, a fully occupied USB3 transmit queue results in: 454.80 KB / (10 Mbit/s / 8 bit/byte) = 363.84 ms of additional latency. This patch adds support for Byte Queue Limits (BQL) [1] to dynamically manage the transmit queue size and reduce latency without sacrificing throughput. Testing was performed on various devices using the usbnet driver for packet transmission: - DELOCK 66045: USB3 to 2.5 GbE adapter (ax88179_178a) - DELOCK 61969: USB2 to 1 GbE adapter (asix) - Quectel RM520: 5G modem (qmi_wwan) - USB2 Android tethering (cdc_ncm) No performance degradation was observed for iperf3 TCP or UDP traffic, while latency for a prioritized ping application was significantly reduced. For example, using the USB3 to 2.5 GbE adapter, which was fully utilized by iperf3 UDP traffic, the prioritized ping was improved from 1.6 ms to 0.6 ms. With the same setup but with a 100 Mbit/s Ethernet connection, the prioritized ping was improved from 35 ms to 5 ms. [1] https://lwn.net/Articles/469652/ Signed-off-by: Simon Schippers <simon.schippers@tu-dortmund.de> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20251106175615.26948-1-simon.schippers@tu-dortmund.de 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 reStructuredText 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.