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In order for the Fq_CoDel algorithm integrated in mac80211 layer to operate effectively to control excessive queueing latency, the CoDel algorithm requires an accurate measure of how long packets stays in the queue, AKA sojourn time. The sojourn time measured at the mac80211 layer doesn't include queueing latency in the lower layer (firmware/hardware) and CoDel expects lower layer to have a short queue. However, most 802.11ac chipsets offload tasks such TX aggregation to firmware or hardware, thus have a deep lower layer queue. Without a mechanism to control the lower layer queue size, packets only stay in mac80211 layer transiently before being sent to firmware queue. As a result, the sojourn time measured by CoDel in the mac80211 layer is almost always lower than the CoDel latency target, hence CoDel does little to control the latency, even when the lower layer queue causes excessive latency. The Byte Queue Limits (BQL) mechanism is commonly used to address the similar issue with wired network interface. However, this method cannot be applied directly to the wireless network interface. "Bytes" is not a suitable measure of queue depth in the wireless network, as the data rate can vary dramatically from station to station in the same network, from a few Mbps to over Gbps. This patch implements an Airtime-based Queue Limit (AQL) to make CoDel work effectively with wireless drivers that utilized firmware/hardware offloading. AQL allows each txq to release just enough packets to the lower layer to form 1-2 large aggregations to keep hardware fully utilized and retains the rest of the frames in mac80211 layer to be controlled by the CoDel algorithm. Signed-off-by: Kan Yan <kyan@google.com> [ Toke: Keep API to set pending airtime internal, fix nits in commit msg ] Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> Link: https://lore.kernel.org/r/20191119060610.76681-4-kyan@google.com Signed-off-by: Johannes Berg <johannes.berg@intel.com> |
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.