Handling of multicast/NO_ACK packets by mac80211 rate scaling is a
mess. Basically, the rule of thumb is that any packet with
IEEE80211_TX_CTL_NO_ACK (including multicasts and broadcasts, which
always have this flag set) should be sent at lowest rate (unless
overridden by radiotap - this is not covered in this patchset), with
no retries.
So, the right thing to do in any rate scaling algorithm:
* Check for IEEE80211_TX_CTL_NO_ACK. No need to check
is_multicast_ether_addr, as multicasts always have NO_ACK set.
* If it is set, select the lowest available rate (unless overridden
by radiotap), with a retry count of 0 (total try count of 1).
However, the actual rate scaling algorithms get this wrong in various ways:
* Minstrel checks for both is_multicast_ether_addr and
IEEE80211_TX_CTL_NO_ACK (redundant, since the former implies the
latter), and sets the rate to the lowest (correct), and the retry
count to the max (wrong).
* PID only checks is_multicast_ether_addr (completely leaving out
unicasts with IEEE80211_TX_CTL_NO_ACK set by e.g. Radiotap), setting
the rate to the lowest (correct). However, the same logic is used for
determining retry count of multicasts as for unicasts (wrong).
* Iwlwifi's rate scaling algorithms behave like PID. In addition,
they appear to not care about retry count at all, which is handled in
the drivers themselves I guess.
* Ath5k's algorithm correctly sets both the rate and the retry count
- but incorrectly bases its checks on is_multicast_ether_addr instead
of IEEE80211_TX_CTL_NO_ACK, again missing unicasts with this flag set.
Most PHYs can gracefully handle this error (with the help of a no-ACK
knob in the PHY TX header that disables retries), but those that have
no such knob, and instead depend on getting a correct retry count of 0
(total try count of 1), such as RTL818x, end up always transmitting
multicast/NO_ACK frames multiple times, as (incorrectly) requested by
the RC algorithm.
Signed-off-by: Gábor Stefanik <netrolller.3d@xxxxxxxxx>
Cc: Felix Fietkau <nbd@xxxxxxxxxxx>
Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Cc: Zhu Yi <yi.zhu@xxxxxxxxx>
Cc: Tomas Winkler <tomas.winkler@xxxxxxxxx>
Cc: Nick Kossifidis <mickflemm@xxxxxxxxx>
Cc: Louis R. Rodriguez <mcgrof@xxxxxxxxx>
Gábor Stefanik (5):
mac80211: Fix handling of retry count of NO_ACK frames in minstrel
mac80211: Fix handling of retry count of NO_ACK frames in PID
iwlwifi: Fix handling of retry count of NO_ACK frames for iwl-{3945|agn}-rs
ath5k: Fix handling of retry count of NO_ACK frames
mac80211: Warn if the rate controller requests retries for a NO_ACK frame
drivers/net/wireless/ath/ath9k/rc.c | 6 +++---
drivers/net/wireless/iwlwifi/iwl-3945-rs.c | 7 ++++---
drivers/net/wireless/iwlwifi/iwl-agn-rs.c | 14 +++++++-------
net/mac80211/rc80211_minstrel.c | 8 +++++---
net/mac80211/rc80211_pid_algo.c | 8 +++++---
net/mac80211/tx.c | 4 ++++
6 files changed, 28 insertions(+), 19 deletions(-)
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