From: Yibo Zhao <yiboz@codeaurora.org>
To: Felix Fietkau <nbd@nbd.name>
Cc: linux-wireless@vger.kernel.org, johannes@sipsolutions.net,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
linux-wireless-owner@vger.kernel.org
Subject: Re: [PATCH] mac80211: rework locking for txq scheduling / airtime fairness
Date: Thu, 10 Oct 2019 10:43:49 +0800 [thread overview]
Message-ID: <b2bded992cb02bad84fc738b7e4b1837@codeaurora.org> (raw)
In-Reply-To: <20190315100335.91445-1-nbd@nbd.name>
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index ca23abbf5c0b..51cc37802439 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -3653,16 +3653,17 @@ EXPORT_SYMBOL(ieee80211_tx_dequeue);
> struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8
> ac)
> {
> struct ieee80211_local *local = hw_to_local(hw);
> + struct ieee80211_txq *ret = NULL;
> struct txq_info *txqi = NULL;
>
> - lockdep_assert_held(&local->active_txq_lock[ac]);
> + spin_lock_bh(&local->active_txq_lock[ac]);
>
> begin:
> txqi = list_first_entry_or_null(&local->active_txqs[ac],
> struct txq_info,
> schedule_order);
> if (!txqi)
> - return NULL;
> + goto out;
>
> if (txqi->txq.sta) {
> struct sta_info *sta = container_of(txqi->txq.sta,
> @@ -3679,21 +3680,25 @@ struct ieee80211_txq
> *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac)
>
>
> if (txqi->schedule_round == local->schedule_round[ac])
> - return NULL;
> + goto out;
>
> list_del_init(&txqi->schedule_order);
> txqi->schedule_round = local->schedule_round[ac];
> - return &txqi->txq;
> + ret = &txqi->txq;
> +
> +out:
> + spin_unlock_bh(&local->active_txq_lock[ac]);
> + return ret;
> }
> EXPORT_SYMBOL(ieee80211_next_txq);
>
> -void ieee80211_return_txq(struct ieee80211_hw *hw,
> - struct ieee80211_txq *txq)
> +void ieee80211_schedule_txq(struct ieee80211_hw *hw,
> + struct ieee80211_txq *txq)
> {
> struct ieee80211_local *local = hw_to_local(hw);
> struct txq_info *txqi = to_txq_info(txq);
>
> - lockdep_assert_held(&local->active_txq_lock[txq->ac]);
> + spin_lock_bh(&local->active_txq_lock[txq->ac]);
>
> if (list_empty(&txqi->schedule_order) &&
> (!skb_queue_empty(&txqi->frags) || txqi->tin.backlog_packets)) {
> @@ -3713,17 +3718,7 @@ void ieee80211_return_txq(struct ieee80211_hw
> *hw,
> list_add_tail(&txqi->schedule_order,
> &local->active_txqs[txq->ac]);
> }
> -}
> -EXPORT_SYMBOL(ieee80211_return_txq);
>
> -void ieee80211_schedule_txq(struct ieee80211_hw *hw,
> - struct ieee80211_txq *txq)
> - __acquires(txq_lock) __releases(txq_lock)
> -{
> - struct ieee80211_local *local = hw_to_local(hw);
> -
> - spin_lock_bh(&local->active_txq_lock[txq->ac]);
> - ieee80211_return_txq(hw, txq);
> spin_unlock_bh(&local->active_txq_lock[txq->ac]);
> }
> EXPORT_SYMBOL(ieee80211_schedule_txq);
> @@ -3736,7 +3731,7 @@ bool ieee80211_txq_may_transmit(struct
> ieee80211_hw *hw,
> struct sta_info *sta;
> u8 ac = txq->ac;
>
> - lockdep_assert_held(&local->active_txq_lock[ac]);
> + spin_lock_bh(&local->active_txq_lock[ac]);
>
> if (!txqi->txq.sta)
> goto out;
> @@ -3766,34 +3761,27 @@ bool ieee80211_txq_may_transmit(struct
> ieee80211_hw *hw,
>
> sta->airtime[ac].deficit += sta->airtime_weight;
> list_move_tail(&txqi->schedule_order, &local->active_txqs[ac]);
> + spin_unlock_bh(&local->active_txq_lock[ac]);
>
> return false;
> out:
> if (!list_empty(&txqi->schedule_order))
> list_del_init(&txqi->schedule_order);
> + spin_unlock_bh(&local->active_txq_lock[ac]);
>
> return true;
> }
> EXPORT_SYMBOL(ieee80211_txq_may_transmit);
>
> void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac)
> - __acquires(txq_lock)
> {
> struct ieee80211_local *local = hw_to_local(hw);
>
> spin_lock_bh(&local->active_txq_lock[ac]);
> local->schedule_round[ac]++;
Hi Felix,
In ath10k, we might have situations like,
CPU0 CPU1
... ieee80211_txq_schedule_start()
... while(ieee80211_next_txq()) {
... driver dequeue packets from
txq
... ieee80211_return_txq()
ieee80211_txq_schedule_start() ...
ieee80211_next_txq() }
driver dequeue packets from txq ieee80211_txq_schedule_end()
ieee80211_return_txq()
ieee80211_txq_schedule_end()
The problem is while CPU1 is looping to dequeue txqs, the schedule_round
which is used to make sure no infinite loop will be changed in CPU0. So
a txq has already been scheduled will be scheduled again then the loop
won't be end at that point as our expected.
> -}
> -EXPORT_SYMBOL(ieee80211_txq_schedule_start);
> -
> -void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
> - __releases(txq_lock)
> -{
> - struct ieee80211_local *local = hw_to_local(hw);
> -
> spin_unlock_bh(&local->active_txq_lock[ac]);
> }
> -EXPORT_SYMBOL(ieee80211_txq_schedule_end);
> +EXPORT_SYMBOL(ieee80211_txq_schedule_start);
>
> void __ieee80211_subif_start_xmit(struct sk_buff *skb,
> struct net_device *dev,
--
Yibo
next prev parent reply other threads:[~2019-10-10 2:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-15 10:03 [PATCH] mac80211: rework locking for txq scheduling / airtime fairness Felix Fietkau
2019-03-15 13:04 ` Toke Høiland-Jørgensen
2019-10-10 2:43 ` Yibo Zhao [this message]
2019-10-10 5:56 ` Felix Fietkau
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