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The hardware can optionally "filter" frames if successive transmissions to a given node (ie, "entry in the keycache") fail. That way the hardware can implement a kind of early abort of all the other frames queued to that destination, rather than simply trying to TX each frame to that destination (and failing.) The background: * If a frame comes back as being filtered, the hardware didn't try to TX it (or it was outside the TX burst opportunity.) So, take it as a hint that some (but not all, see below) frames to the destination may be filtered. * If the CLRDMASK bit is set in a TX descriptor, the "filter to this destination" bit in the keycache entry is cleared and TX to that host will be unconditionally retried. * Right now everything has the CLRDMASK bit set, so filtered frames tend to be aggregates and frames that fall outside of the WME burst window. It was a bit worse in the past as I had messed up the TX flags and CLRDMASK wasn't being set on aggregate frames. The annoying bits: * It's easy (ish) to do for aggregate session frames - firstly, they can be retried in any order as long as they're within the BAW, and there's already a bunch of infrastructure tracking how many frames the TID has queued to the hardware (tid->hwq_depth.) However, for frames that bypassed the software queue, hwq_depth doesn't get incremented. I'll fix that in a subsequent commit. * For non-aggregate session frames, the only retries that can occur are ones for sequence numbers that hvaen't successfully been TXed yet. Since there's no re-ordering going on in non-aggregate sessions, if any subsequent seqno frames make it out, any filtered frames before that seqno need to be dropped. Hence why this initially is just for aggregate session frames. * Since there may be intermediary frames to the destination that have CLRDMASK set - for example, any directly dispatched management frames to that destination - it's possible that there will be some filtered frames followed up by some non filtered frames. Thus, it can't be assumed that once you see a filtered frame for the given destination node, all subsequent frames for all TIDs will be filtered. Ok, with that in mind: * Create a per-TID filtered frame queue for frames that the hardware returns as filtered. * Track filtered frames per-tid, rather than per-node. It just makes the locking much easier. * When a filtered frame appears in the completion function, the node transitions to "filtered", and all subsequent completed error frames (filtered or otherwise) are put on the filtered frame queue. The TID is paused once (during the transition from non-filtered to filtered). * If a filtered frame retry count exceeds SWMAX_RETRIES, a BAR should be sent. * Once all the frames queued to the hardware for the given filtered frame TID, transition back from filtered frame to non-filtered frame, which means pre-pending all the filtered frames onto the head of the software queue, clearing the filtered frame state and unpausing the TID. Things get quite hairy around handling completion (aggr, non-aggr, norm, direct-dispatched frames to a hardware queue); whether it's an "error", "cleanup" or "BAR" state as well as filtered, which order to do things in (eg do filtered BEFORE checking for BAR, as the filter completion may be needed to actually transmit a BAR frame.) This work has definitely reminded me that I have to tidy up all the locking and remove some of the ridiculous lock/unlock/lock/unlock going on in the completion functions. It's also reminded me that I should really split out TID versus hardware TXQ locking, even if the underlying locking is still the destination hardware TXQ. Finally, this is all pre-requisite for working on AP mode power save support (PS-POLL, uAPSD) as well as improving performance to misbehaving nodes (as they can transition into filter mode, stopping any TX until everything has caught up.) Finally (ish) - this should also be done for non-aggregate sessions as there are still plenty of laptops and mobile devices that don't speak 802.11n but do wish for stable, useful power save AP support where packets aren't simply dropped. This requires software retransmission for non-aggregate sessions to be implemented, which includes the caveats I've mentioned above. Finally finally - this doesn't yet do anything about the CLRDMASK bit in the TX descriptor. That's still unconditionally set to 1. I'll debug the current work (mostly ensuring I haven't busted up the hairy transitions between BAR, filtered, error (all frames in an aggregate failing) and cleanup (when transitioning from aggregation -> non-aggregation.)) Finally finally finally - this is all original work by yours truely, rather than ported from the Atheros internal driver codebase or Linux ath9k. Tested: * AR9280, AR5416 in STA mode * AR9280, AR9130 in hostap mode * Lots and lots of iperf testing in very marginal and non-marginal conditions, complete with inducing filtered frames + BAR TX conditions. |
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| gnu | ||
| include | ||
| kerberos5 | ||
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| release | ||
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| COPYRIGHT | ||
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| Makefile | ||
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| 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