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Felix Fietkau 48cb39522a mac80211: minstrel_ht: improve rate probing for devices with static fallback
On some devices that only support static rate fallback tables sending rate
control probing packets can be really expensive.
Probing lower rates can already hurt throughput quite a bit. What hurts even
more is the fact that on mt76x0/mt76x2, single probing packets can only be
forced by directing packets at a different internal hardware queue, which
causes some heavy reordering and extra latency.
The reordering issue is mainly problematic while pushing lots of packets to
a particular station. If there is little activity, the overhead of probing is
neglegible.

The static fallback behavior is designed to pretty much only handle rate
control algorithms that use only a very limited set of rates on which the
algorithm switches up/down based on packet error rate.

In order to better support that kind of hardware, this patch implements a
different approach to rate probing where it switches to a slightly higher rate,
waits for tx status feedback, then updates the stats and switches back to
the new max throughput rate. This only triggers above a packet rate of 100
per stats interval (~50ms).
For that kind of probing, the code has to reduce the set of probing rates
a lot more compared to single packet probing, so it uses only one packet
per MCS group which is either slightly faster, or as close as possible to
the max throughput rate.
This allows switching between similar rates with different numbers of
streams. The algorithm assumes that the hardware will work its way lower
within an MCS group in case of retransmissions, so that lower rates don't
have to be probed by the high packets per second rate probing code.

To further reduce the search space, it also does not probe rates with lower
channel bandwidth than the max throughput rate.

At the moment, these changes will only affect mt76x0/mt76x2.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20190820095449.45255-4-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
2019-08-21 11:10:13 +02:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-08-19 11:54:03 -07:00
block
certs
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Documentation Documentation: net: mlx5: Devlink health documentation updates 2019-08-20 13:08:18 -07:00
drivers nl80211: Add support for EDMG channels 2019-08-21 11:07:35 +02:00
fs for-5.3-rc4-tag 2019-08-18 09:51:48 -07:00
include nl80211: Add support for EDMG channels 2019-08-21 11:07:35 +02:00
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kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-08-19 11:54:03 -07:00
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net mac80211: minstrel_ht: improve rate probing for devices with static fallback 2019-08-21 11:10:13 +02:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-08-19 11:54:03 -07:00
scripts Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-08-19 11:54:03 -07:00
security
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tools tc-testing: concurrency: wrap piped rule update commands 2019-08-19 18:19:48 -07:00
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MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-08-19 11:54:03 -07:00
Makefile Linux 5.3-rc5 2019-08-18 14:31:08 -07:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.