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Date:   Thu, 04 Apr 2019 12:43:43 +0800
From:   Yibo Zhao <yiboz@codeaurora.org>
To:     =?UTF-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
Cc:     make-wifi-fast@lists.bufferbloat.net,
        linux-wireless@vger.kernel.org, Felix Fietkau <nbd@nbd.name>,
        Rajkumar Manoharan <rmanohar@codeaurora.org>,
        Kan Yan <kyan@google.com>, linux-wireless-owner@vger.kernel.org
Subject: Re: [RFC/RFT] mac80211: Switch to a virtual time-based airtime
 scheduler
In-Reply-To: <abb711cc66cf83832684225e35591d03@codeaurora.org>
References: <20190215170512.31512-1-toke@redhat.com>
 <abb711cc66cf83832684225e35591d03@codeaurora.org>
Message-ID: <af10fe052347e69d92b0ff65a45f41f3@codeaurora.org>
User-Agent: Roundcube Webmail/1.2.5
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

On 2019-04-04 12:41, Yibo Zhao wrote:
> On 2019-02-16 01:05, Toke Høiland-Jørgensen wrote:
>> This switches the airtime scheduler in mac80211 to use a virtual 
>> time-based
>> scheduler instead of the round-robin scheduler used before. This has a
>> couple of advantages:
>> 
>> - No need to sync up the round-robin scheduler in firmware/hardware 
>> with
>>   the round-robin airtime scheduler.
>> 
>> - If several stations are eligible for transmission we can schedule 
>> both of
>>   them; no need to hard-block the scheduling rotation until the head 
>> of the
>>   queue has used up its quantum.
>> 
>> - The check of whether a station is eligible for transmission becomes
>>   simpler (in ieee80211_txq_may_transmit()).
>> 
>> The drawback is that scheduling becomes slightly more expensive, as we 
>> need
>> to maintain an rbtree of TXQs sorted by virtual time. This means that
>> ieee80211_register_airtime() becomes O(logN) in the number of 
>> currently
>> scheduled TXQs. However, hopefully this number rarely grows too big 
>> (it's
>> only TXQs currently backlogged, not all associated stations), so it
>> shouldn't be too big of an issue.
>> 
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> ---
>> @@ -1831,18 +1830,32 @@ void ieee80211_sta_register_airtime(struct
>> ieee80211_sta *pubsta, u8 tid,
>>  {
>>  	struct sta_info *sta = container_of(pubsta, struct sta_info, sta);
>>  	struct ieee80211_local *local = sta->sdata->local;
>> +	struct ieee80211_txq *txq = sta->sta.txq[tid];
>>  	u8 ac = ieee80211_ac_from_tid(tid);
>> -	u32 airtime = 0;
>> +	u64 airtime = 0, weight_sum;
>> +
>> +	if (!txq)
>> +		return;
>> 
>>  	if (sta->local->airtime_flags & AIRTIME_USE_TX)
>>  		airtime += tx_airtime;
>>  	if (sta->local->airtime_flags & AIRTIME_USE_RX)
>>  		airtime += rx_airtime;
>> 
>> +	/* Weights scale so the unit weight is 256 */
>> +	airtime <<= 8;
>> +
>>  	spin_lock_bh(&local->active_txq_lock[ac]);
>> +
>>  	sta->airtime[ac].tx_airtime += tx_airtime;
>>  	sta->airtime[ac].rx_airtime += rx_airtime;
>> -	sta->airtime[ac].deficit -= airtime;
>> +
>> +	weight_sum = local->airtime_weight_sum[ac] ?: sta->airtime_weight;
>> +
>> +	local->airtime_v_t[ac] += airtime / weight_sum;
> Hi Toke,
> 
> it looks like local->airtime_v_t acts like a Tx criteria. Only the
> stations with less airtime than that are valid for Tx. That means
> there are situations, like 50 clients, that some of the stations can
> be used to Tx when putting next_txq in the loop. Am I right?
> 
>> +	sta->airtime[ac].v_t += airtime / sta->airtime_weight;
> 
Another question, any plan for taking v_t overflow situation into
consideration? u64 might be enough for low throughput products but not
sure for high end products. Something like below:
u64 prev = sta->airtime[ac].v_t;

      if ()

>> +	ieee80211_resort_txq(&local->hw, txq);
>> +
>>  	spin_unlock_bh(&local->active_txq_lock[ac]);
>>  }
>>  EXPORT_SYMBOL(ieee80211_sta_register_airtime);
>> diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
>> index 05647d835894..4b901a2a998e 100644
>> --- a/net/mac80211/sta_info.h
>> +++ b/net/mac80211/sta_info.h
>> @@ -130,11 +130,12 @@ enum ieee80211_agg_stop_reason {
>>  /* Debugfs flags to enable/disable use of RX/TX airtime in scheduler 
>> */
>>  #define AIRTIME_USE_TX		BIT(0)
>>  #define AIRTIME_USE_RX		BIT(1)
>> +#define AIRTIME_GRACE 500 /* usec of grace period before reset */
>> 
>>  struct airtime_info {
>>  	u64 rx_airtime;
>>  	u64 tx_airtime;
>> -	s64 deficit;
>> +	u64 v_t;
>>  };
>> 
>>  struct sta_info;
>> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
>> index 61c7ea9de2cc..8e125df8ade0 100644
>> --- a/net/mac80211/tx.c
>> +++ b/net/mac80211/tx.c
>> @@ -1449,7 +1449,7 @@ void ieee80211_txq_init(struct
>> ieee80211_sub_if_data *sdata,
>>  	codel_vars_init(&txqi->def_cvars);
>>  	codel_stats_init(&txqi->cstats);
>>  	__skb_queue_head_init(&txqi->frags);
>> -	INIT_LIST_HEAD(&txqi->schedule_order);
>> +	RB_CLEAR_NODE(&txqi->schedule_order);
>> 
>>  	txqi->txq.vif = &sdata->vif;
>> 
>> @@ -1493,9 +1493,7 @@ void ieee80211_txq_purge(struct ieee80211_local 
>> *local,
>>  	ieee80211_purge_tx_queue(&local->hw, &txqi->frags);
>>  	spin_unlock_bh(&fq->lock);
>> 
>> -	spin_lock_bh(&local->active_txq_lock[txqi->txq.ac]);
>> -	list_del_init(&txqi->schedule_order);
>> -	spin_unlock_bh(&local->active_txq_lock[txqi->txq.ac]);
>> +	ieee80211_unschedule_txq(&local->hw, &txqi->txq);
>>  }
>> 
>>  void ieee80211_txq_set_params(struct ieee80211_local *local)
>> @@ -3640,126 +3638,191 @@ 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 rb_node *node = local->schedule_pos[ac];
>>  	struct txq_info *txqi = NULL;
>> +	bool first = false;
>> 
>>  	lockdep_assert_held(&local->active_txq_lock[ac]);
>> 
>> - begin:
>> -	txqi = list_first_entry_or_null(&local->active_txqs[ac],
>> -					struct txq_info,
>> -					schedule_order);
>> -	if (!txqi)
>> +	if (!node) {
>> +		node = rb_first_cached(&local->active_txqs[ac]);
>> +		first = true;
>> +	} else
>> +		node = rb_next(node);
>> +
>> +	if (!node)
>>  		return NULL;
>> 
>> +	txqi = container_of(node, struct txq_info, schedule_order);
>> +
>>  	if (txqi->txq.sta) {
>>  		struct sta_info *sta = container_of(txqi->txq.sta,
>>  						struct sta_info, sta);
>> 
>> -		if (sta->airtime[txqi->txq.ac].deficit < 0) {
>> -			sta->airtime[txqi->txq.ac].deficit +=
>> -				sta->airtime_weight;
>> -			list_move_tail(&txqi->schedule_order,
>> -				       &local->active_txqs[txqi->txq.ac]);
>> -			goto begin;
>> +		if (sta->airtime[ac].v_t > local->airtime_v_t[ac]) {
>> +			if (first)
>> +				local->airtime_v_t[ac] = sta->airtime[ac].v_t;
>> +			else
>> +				return NULL;
>>  		}
>>  	}
>> 
>> 
>> -	if (txqi->schedule_round == local->schedule_round[ac])
>> -		return NULL;
>> -
>> -	list_del_init(&txqi->schedule_order);
>> -	txqi->schedule_round = local->schedule_round[ac];
>> +	local->schedule_pos[ac] = node;
>>  	return &txqi->txq;
>>  }
>>  EXPORT_SYMBOL(ieee80211_next_txq);
>> 
>> -void ieee80211_return_txq(struct ieee80211_hw *hw,
>> +static void __ieee80211_insert_txq(struct rb_root_cached *root,
>> +				   struct txq_info *txqi, u8 ac)
>> +{
>> +	struct rb_node **new = &root->rb_root.rb_node;
>> +	struct rb_node *parent = NULL;
>> +	struct txq_info *__txqi;
>> +	bool leftmost = true;
>> +
>> +	while (*new) {
>> +		parent = *new;
>> +		__txqi = rb_entry(parent, struct txq_info, schedule_order);
>> +
>> +		if (!txqi->txq.sta) {
>> +			/* new txqi has no sta - insert to the left */
>> +			new = &parent->rb_left;
>> +		} else if (!__txqi->txq.sta) {
>> +			/* existing txqi has no sta - insert to the right */
>> +			new = &parent->rb_right;
>> +			leftmost = false;
>> +		} else {
>> +			struct sta_info *old_sta = container_of(__txqi->txq.sta,
>> +								struct sta_info,
>> +								sta);
>> +			struct sta_info *new_sta = container_of(txqi->txq.sta,
>> +								struct sta_info,
>> +								sta);
>> +
>> +			if (new_sta->airtime[ac].v_t <= old_sta->airtime[ac].v_t)
>> +				new = &parent->rb_left;
>> +			else {
>> +				new = &parent->rb_right;
>> +				leftmost = false;
>> +			}
>> +
>> +		}
>> +	}
>> +
>> +	rb_link_node(&txqi->schedule_order, parent, new);
>> +	rb_insert_color_cached(&txqi->schedule_order, root, leftmost);
>> +}
>> +
>> +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);
>> +	struct txq_info *txqi = to_txq_info(txq);
>> +	u8 ac = txq->ac;
>> +
>> +	spin_lock_bh(&local->active_txq_lock[ac]);
>> +
>> +	if (!RB_EMPTY_NODE(&txqi->schedule_order))
>> +		goto out;
>> +
>> +	if (txq->sta) {
>> +		struct sta_info *sta = container_of(txq->sta,
>> +						    struct sta_info, sta);
>> +
>> +		local->airtime_weight_sum[ac] += sta->airtime_weight;
>> +		if (local->airtime_v_t[ac] > AIRTIME_GRACE)
>> +			sta->airtime[ac].v_t = max(local->airtime_v_t[ac] - AIRTIME_GRACE,
>> +						   sta->airtime[ac].v_t);
>> +	}
>> +
>> +	__ieee80211_insert_txq(&local->active_txqs[ac], txqi, ac);
>> +
>> + out:
>> +	spin_unlock_bh(&local->active_txq_lock[ac]);
>> +}
>> +EXPORT_SYMBOL(ieee80211_schedule_txq);
>> +
>> +void ieee80211_resort_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);
>> +	u8 ac = txq->ac;
>> +
>> +	if (!RB_EMPTY_NODE(&txqi->schedule_order)) {
>> +		rb_erase_cached(&txqi->schedule_order,
>> +				&local->active_txqs[ac]);
>> +		RB_CLEAR_NODE(&txqi->schedule_order);
>> +		__ieee80211_insert_txq(&local->active_txqs[ac], txqi, ac);
>> +	}
>> +}
>> +
>> +static void __ieee80211_unschedule_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);
>> +	u8 ac = txq->ac;
>> 
>>  	lockdep_assert_held(&local->active_txq_lock[txq->ac]);
>> 
>> -	if (list_empty(&txqi->schedule_order) &&
>> -	    (!skb_queue_empty(&txqi->frags) || txqi->tin.backlog_packets)) {
>> -		/* If airtime accounting is active, always enqueue STAs at the
>> -		 * head of the list to ensure that they only get moved to the
>> -		 * back by the airtime DRR scheduler once they have a negative
>> -		 * deficit. A station that already has a negative deficit will
>> -		 * get immediately moved to the back of the list on the next
>> -		 * call to ieee80211_next_txq().
>> -		 */
>> -		if (txqi->txq.sta &&
>> -		    wiphy_ext_feature_isset(local->hw.wiphy,
>> -					    NL80211_EXT_FEATURE_AIRTIME_FAIRNESS))
>> -			list_add(&txqi->schedule_order,
>> -				 &local->active_txqs[txq->ac]);
>> -		else
>> -			list_add_tail(&txqi->schedule_order,
>> -				      &local->active_txqs[txq->ac]);
>> +	if (RB_EMPTY_NODE(&txqi->schedule_order))
>> +		return;
>> +
>> +	if (txq->sta) {
>> +		struct sta_info *sta = container_of(txq->sta,
>> +						    struct sta_info, sta);
>> +
>> +		local->airtime_weight_sum[ac] -= sta->airtime_weight;
>>  	}
>> +
>> +	rb_erase_cached(&txqi->schedule_order,
>> +			&local->active_txqs[txq->ac]);
>> +	RB_CLEAR_NODE(&txqi->schedule_order);
>>  }
>> -EXPORT_SYMBOL(ieee80211_return_txq);
>> 
>> -void ieee80211_schedule_txq(struct ieee80211_hw *hw,
>> -			    struct ieee80211_txq *txq)
>> +void ieee80211_unschedule_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);
>> +	__ieee80211_unschedule_txq(hw, txq);
>>  	spin_unlock_bh(&local->active_txq_lock[txq->ac]);
>>  }
>> -EXPORT_SYMBOL(ieee80211_schedule_txq);
>> +
>> +void ieee80211_return_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]);
>> +
>> +	if (!RB_EMPTY_NODE(&txqi->schedule_order) &&
>> +	    (skb_queue_empty(&txqi->frags) && !txqi->tin.backlog_packets))
>> +		__ieee80211_unschedule_txq(hw, txq);
>> +}
>> +EXPORT_SYMBOL(ieee80211_return_txq);
>> 
>>  bool ieee80211_txq_may_transmit(struct ieee80211_hw *hw,
>>  				struct ieee80211_txq *txq)
>>  {
>>  	struct ieee80211_local *local = hw_to_local(hw);
>> -	struct txq_info *iter, *tmp, *txqi = to_txq_info(txq);
>> +	struct txq_info *txqi = to_txq_info(txq);
>>  	struct sta_info *sta;
>>  	u8 ac = txq->ac;
>> 
>>  	lockdep_assert_held(&local->active_txq_lock[ac]);
>> 
>>  	if (!txqi->txq.sta)
>> -		goto out;
>> -
>> -	if (list_empty(&txqi->schedule_order))
>> -		goto out;
>> -
>> -	list_for_each_entry_safe(iter, tmp, &local->active_txqs[ac],
>> -				 schedule_order) {
>> -		if (iter == txqi)
>> -			break;
>> -
>> -		if (!iter->txq.sta) {
>> -			list_move_tail(&iter->schedule_order,
>> -				       &local->active_txqs[ac]);
>> -			continue;
>> -		}
>> -		sta = container_of(iter->txq.sta, struct sta_info, sta);
>> -		if (sta->airtime[ac].deficit < 0)
>> -			sta->airtime[ac].deficit += sta->airtime_weight;
>> -		list_move_tail(&iter->schedule_order, &local->active_txqs[ac]);
>> -	}
>> +		return true;
>> 
>>  	sta = container_of(txqi->txq.sta, struct sta_info, sta);
>> -	if (sta->airtime[ac].deficit >= 0)
>> -		goto out;
>> -
>> -	sta->airtime[ac].deficit += sta->airtime_weight;
>> -	list_move_tail(&txqi->schedule_order, &local->active_txqs[ac]);
>> -
>> -	return false;
>> -out:
>> -	if (!list_empty(&txqi->schedule_order))
>> -		list_del_init(&txqi->schedule_order);
>> -
>> -	return true;
>> +	return (sta->airtime[ac].v_t <= local->airtime_v_t[ac]);
>>  }
>>  EXPORT_SYMBOL(ieee80211_txq_may_transmit);
>> 
>> @@ -3769,7 +3832,6 @@ void ieee80211_txq_schedule_start(struct
>> ieee80211_hw *hw, u8 ac)
>>  	struct ieee80211_local *local = hw_to_local(hw);
>> 
>>  	spin_lock_bh(&local->active_txq_lock[ac]);
>> -	local->schedule_round[ac]++;
>>  }
>>  EXPORT_SYMBOL(ieee80211_txq_schedule_start);
>> 
>> @@ -3778,6 +3840,7 @@ void ieee80211_txq_schedule_end(struct
>> ieee80211_hw *hw, u8 ac)
>>  {
>>  	struct ieee80211_local *local = hw_to_local(hw);
>> 
>> +	local->schedule_pos[ac] = NULL;
>>  	spin_unlock_bh(&local->active_txq_lock[ac]);
>>  }
>>  EXPORT_SYMBOL(ieee80211_txq_schedule_end);

-- 
Yibo