freebsd kernel with SKQ
af7893e0d4
My changed had some rather significant behavioural changes to throughput. The two issues I noticed: * With if_start and the ifnet mbuf queue, any temporary latency would get eaten up by some mbufs being queued. With ath_transmit() queuing things to ath_buf's, I'd only get 512 TX buffers before I couldn't queue any further frames. * There's also some non-zero latency involved with TX being pushed into a taskqueue via direct dispatch. Any time the scheduler didn't immediately schedule the ath TX task would cause extra latency. Various 1ge/10ge drivers implement both direct dispatch (if the TX lock can be acquired) and deferred task transmission (if the TX lock can't be acquired), with frames being pushed into a drbd queue. I'll have to do this at some point, but until I figure out how to deal with 802.11 fragments, I'll have to wait a while longer. So what I saw: * lots of extra latency, specially under load - if the taskqueue wasn't immediately scheduled, things went pear shaped; * any extra latency would result in TX ath_buf's taking their sweet time being replenished, so any further calls to ath_transmit() would drop mbufs. * .. yes, there's no explicit backpressure here - things are just dropped. Eek. With this, the general performance has gone up, but those subtle if_start() related race conditions are back. For some reason, this is doubly-obvious with the AR5416 NIC and I don't quite understand why yet. There's an unrelated issue with AR5416 performance in STA mode (it's fine in AP mode when bridging frames, weirdly..) that requires a little further investigation. Specifically - it works fine on a Lenovo T40 (single core CPU) running a March 2012 9-STABLE kernel, but a Lenovo T60 (dual core) running an early November 2012 kernel behaves very poorly. The same hardware with an AR9160 or AR9280 behaves perfectly. |
||
|---|---|---|
| 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