freebsd with flexible iflib nic queues
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Adrian Chadd 629ce2188a Implement "holding buffers" per TX queue rather than globally.
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.)
2013-03-14 06:20:02 +00:00
bin sh: When executing a trap, keep exit status along with evalskip. 2013-03-03 17:33:59 +00:00
cddl Fix error in r247960: actually assign the basename to match.iim_file. 2013-03-07 22:43:50 +00:00
contrib Merge upstream r634:646: correctly parse mixed quoted / unquoted text. 2013-03-04 18:51:53 +00:00
crypto Unlike OpenBSD's, our setusercontext() will intentionally ignore the user's 2013-03-13 09:41:55 +00:00
etc Finish portalfs removal. 2013-03-10 17:33:41 +00:00
games Remove fortunes-o from the base system. Debating what does or does not 2013-03-12 12:35:02 +00:00
gnu kgdb enhancements! 2013-02-19 02:09:18 +00:00
include Import libyaml 0.1.4 into vendor 2013-03-03 23:26:17 +00:00
kerberos5 Add -lheimntlm to LDADD directly. 2013-02-11 09:45:24 +00:00
lib libc: Avoid SIGPIPE when nscd closes the connection unexpectedly. 2013-03-13 18:38:18 +00:00
libexec Map libraries linked with -Ttext-segment=base_addr at base_addr. 2013-02-27 09:34:09 +00:00
release the NO_PAM option has been finally removed in favor of WITHOUT_PAM. 2013-02-18 02:08:41 +00:00
rescue Disconnect non-MPSAFE SMBFS from the build in preparation for dropping 2012-10-18 12:04:56 +00:00
sbin Add legacy support to geom raid to create a /dev/arX device for support 2013-03-08 20:07:32 +00:00
secure Merge OpenSSL 1.0.1e. 2013-02-13 23:07:20 +00:00
share vinum isn't a new product. 2013-03-13 22:27:01 +00:00
sys Implement "holding buffers" per TX queue rather than globally. 2013-03-14 06:20:02 +00:00
tools Fix compile warning by including ctype.h for isdigit(). 2013-03-05 19:37:29 +00:00
usr.bin No need to call an external program. 2013-03-13 22:50:14 +00:00
usr.sbin - Make the FreeBSD's USB library compile under Linux. 2013-03-13 12:23:14 +00:00
COPYRIGHT Happy New Year 2013! 2012-12-31 11:22:55 +00:00
LOCKS Test commit to make sure commit mail works after moving the server. 2012-12-29 16:03:23 +00:00
MAINTAINERS MAINTAINERS: Document my maintainership of sh(1). 2013-03-03 15:02:56 +00:00
Makefile Import OpenSSL 1.0.1e. 2013-02-13 22:15:56 +00:00
Makefile.inc1 In all situations where we need to bootstrap yacc, we also need to 2013-02-25 22:25:56 +00:00
ObsoleteFiles.inc Ports are no more exported via cvsup, remove cvsup examples and documentation refering to ports 2013-03-11 10:48:26 +00:00
README Import libyaml 0.1.4 into vendor 2013-03-03 23:26:17 +00:00
UPDATING Merge r247814 from x86 modulo whitespace bug: 2013-03-08 13:11:45 +00:00

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