2022-06-25 21:24:41

by Felix Fietkau

Subject: [PATCH 3/7] mac80211: consider aql_tx_pending when checking airtime deficit

When queueing packets for a station, deficit only gets added once the packets
have been transmitted, which could be much later. During that time, a lot of
temporary unfairness could happen, which could lead to bursty behavior.
Fix this by subtracting the aql_tx_pending when checking the deficit in tx
scheduling.

Signed-off-by: Felix Fietkau <[email protected]>
---
net/mac80211/tx.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index a615cadf7728..0509486ac40a 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3800,6 +3800,13 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
}
EXPORT_SYMBOL(ieee80211_tx_dequeue);

+static inline s32 ieee80211_sta_deficit(struct sta_info *sta, u8 ac)
+{
+ struct airtime_info *air_info = &sta->airtime[ac];
+
+ return air_info->deficit - atomic_read(&air_info->aql_tx_pending);
+}
+
struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
{
struct ieee80211_local *local = hw_to_local(hw);
@@ -3830,7 +3837,7 @@ struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
struct sta_info *sta = container_of(txqi->txq.sta,
struct sta_info, sta);
bool aql_check = ieee80211_txq_airtime_check(hw, &txqi->txq);
- s32 deficit = sta->airtime[txqi->txq.ac].deficit;
+ s32 deficit = ieee80211_sta_deficit(sta, txqi->txq.ac);

if (aql_check)
found_eligible_txq = true;
@@ -3955,7 +3962,7 @@ bool ieee80211_txq_may_transmit(struct ieee80211_hw *hw,
continue;
}
sta = container_of(iter->txq.sta, struct sta_info, sta);
- if (sta->airtime[ac].deficit < 0)
+ if (ieee80211_sta_deficit(sta, ac) < 0)
sta->airtime[ac].deficit += sta->airtime_weight;
list_move_tail(&iter->schedule_order, &local->active_txqs[ac]);
}
--
2.36.1

2022-06-27 15:06:55

by Toke Høiland-Jørgensen

Subject: Re: [PATCH 3/7] mac80211: consider aql_tx_pending when checking airtime deficit

Felix Fietkau <[email protected]> writes:

> When queueing packets for a station, deficit only gets added once the packets
> have been transmitted, which could be much later. During that time, a lot of
> temporary unfairness could happen, which could lead to bursty behavior.
> Fix this by subtracting the aql_tx_pending when checking the deficit in tx
> scheduling.
>
> Signed-off-by: Felix Fietkau <[email protected]>

Acked-by: Toke Høiland-Jørgensen <[email protected]>