freebsd with flexible iflib nic queues
470a7f4191
implementing parallel TX and TX/RX completion can be done without simply abusing long-held locks. Right now, multiple concurrent ath_start() entries can result in frames being dequeued out of order. Well, they're dequeued in order fine, but if there's any preemption or race between CPUs between: * removing the frame from the ifnet, and * calling and runningath_tx_start(), until the frame is placed on a software or hardware TXQ Then although dequeueing the frame is in-order, queueing it to the hardware may be out of order. This is solved in a lot of other drivers by just holding a TX lock over a rather long period of time. This lets them continue to direct dispatch without races between dequeue and hardware queue. Note to observers: if_transmit() doesn't necessarily solve this. It removes the ifnet from the main path, but the same issue exists if there's some intermediary queue (eg a bufring, which as an aside also may pull in ifnet when you're using ALTQ.) So, until I can sit down and code up a much better way of doing parallel TX, I'm going to leave the TX path using a deferred taskqueue task. What I will likely head towards is doing a direct dispatch to hardware or software via if_transmit(), but it'll require some driver changes to allow queues to be made without using the really large ath_buf / ath_desc entries. TODO: * Look at how feasible it'll be to just do direct dispatch to ath_tx_start() from if_transmit(), avoiding doing _any_ intermediary serialisation into a global queue. This may break ALTQ for example, so I have to be delicate. * It's quite likely that I should break up ath_tx_start() so it deposits frames onto the software queues first, and then only fill in the 802.11 fields when it's being queued to the hardware. That will make the if_transmit() -> software queue path very quick and lightweight. * This has some very bad behaviour when using ACPI and Cx states. I'll do some subsequent analysis using KTR and schedgraph and file a follow-up PR or two. PR: kern/168649 |
||
|---|---|---|
| bin | ||
| cddl | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| 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