freebsd kernel with SKQ
48088f84e7
When working on TDMA, Sam Leffler found that the MAC DMA hardware would re-read the last TX descriptor when getting ready to transmit the next one. Thus the whole ATH_BUF_BUSY came into existance - the descriptor must be left alone (very specifically the link pointer must be maintained) until the hardware has moved onto the next frame. He saw this in TDMA because the MAC would be frequently stopping during active transmit (ie, when it wasn't its turn to transmit.) Fast-forward to today. It turns out that this is a problem not with a single MAC DMA instance, but with each QCU (from 0->9). They each maintain separate descriptor pointers and will re-read the last descriptor when starting to transmit the next. So when your AP is busy transmitting from multiple TX queues, you'll (more) frequently see one QCU stopped, waiting for a higher-priority QCU to finsh transmitting, before it'll go ahead and continue. If you mess up the descriptor (ie by freeing it) then you're short of luck. Thanks to rpaulo for sticking with me whilst I diagnosed this issue that he was quite reliably triggering in his environment. This is a reimplementation; it doesn't have anything in common with the ath9k or the Qualcomm Atheros reference driver. Now - it in theory doesn't apply on the EDMA chips, as long as you push one complete frame into the FIFO at a time. But the MAC can DMA from a list of frames pushed into the hardware queue (ie, you concat 'n' frames together with link pointers, and then push the head pointer into the TXQ FIFO.) Since that's likely how I'm going to implement CABQ handling in hostap mode, it's likely that I will end up teaching the EDMA TX completion code about busy buffers, just to be "sure" this doesn't creep up. Tested - iperf ap->sta and sta->ap (with both sides running this code): * AR5416 STA * AR9160/AR9220 hostap To validate that it doesn't break the EDMA (FIFO) chips: * AR9380, AR9485, AR9462 STA Using iperf with the -S <tos byte decimal value> to set the TCP client side DSCP bits, mapping to different TIDs and thus different TX queues. TODO: * Make this work on the EDMA chips, if we end up pushing lists of frames to the hardware (eg how we eventually will handle cabq in hostap/ibss mode.) |
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| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
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| secure | ||
| share | ||
| sys | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| ObsoleteFiles.inc | ||
| README | ||
| UPDATING | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``world'' target should only be used in cases where the source tree has not changed from the currently running version. See: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you might need to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/<arch>/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/user commands. cddl Various commands and libraries under the Common Development and Distribution License. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc. games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberos5 Kerberos5 (Heimdal) package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. rescue Build system for statically linked /rescue utilities. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html