Commit 3ace10f5 authored by Kan Yan's avatar Kan Yan Committed by Johannes Berg
Browse files

mac80211: Implement Airtime-based Queue Limit (AQL) 



In order for the Fq_CoDel algorithm integrated in mac80211 layer to operate
effectively to control excessive queueing latency, the CoDel algorithm
requires an accurate measure of how long packets stays in the queue, AKA
sojourn time. The sojourn time measured at the mac80211 layer doesn't
include queueing latency in the lower layer (firmware/hardware) and CoDel
expects lower layer to have a short queue. However, most 802.11ac chipsets
offload tasks such TX aggregation to firmware or hardware, thus have a deep
lower layer queue.

Without a mechanism to control the lower layer queue size, packets only
stay in mac80211 layer transiently before being sent to firmware queue.
As a result, the sojourn time measured by CoDel in the mac80211 layer is
almost always lower than the CoDel latency target, hence CoDel does little
to control the latency, even when the lower layer queue causes excessive
latency.

The Byte Queue Limits (BQL) mechanism is commonly used to address the
similar issue with wired network interface. However, this method cannot be
applied directly to the wireless network interface. "Bytes" is not a
suitable measure of queue depth in the wireless network, as the data rate
can vary dramatically from station to station in the same network, from a
few Mbps to over Gbps.

This patch implements an Airtime-based Queue Limit (AQL) to make CoDel work
effectively with wireless drivers that utilized firmware/hardware
offloading. AQL allows each txq to release just enough packets to the lower
layer to form 1-2 large aggregations to keep hardware fully utilized and
retains the rest of the frames in mac80211 layer to be controlled by the
CoDel algorithm.

Signed-off-by: default avatarKan Yan <kyan@google.com>
[ Toke: Keep API to set pending airtime internal, fix nits in commit msg ]
Signed-off-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20191119060610.76681-4-kyan@google.com


Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
parent db3e1c40

include/net/cfg80211.h

+7 −0
Original line number Diff line number Diff line
@@ -2606,6 +2606,13 @@ enum wiphy_params_flags { 


#define IEEE80211_DEFAULT_AIRTIME_WEIGHT	256



/* The per TXQ device queue limit in airtime */

#define IEEE80211_DEFAULT_AQL_TXQ_LIMIT_L	5000

#define IEEE80211_DEFAULT_AQL_TXQ_LIMIT_H	12000



/* The per interface airtime threshold to switch to lower queue limit */

#define IEEE80211_AQL_THRESHOLD			24000



/**

 * struct cfg80211_pmksa - PMK Security Association

 *

include/net/mac80211.h

+12 −0
Original line number Diff line number Diff line
@@ -5565,6 +5565,18 @@ void ieee80211_send_eosp_nullfunc(struct ieee80211_sta *pubsta, int tid); 
void ieee80211_sta_register_airtime(struct ieee80211_sta *pubsta, u8 tid,

				    u32 tx_airtime, u32 rx_airtime);



/**

 * ieee80211_txq_airtime_check - check if a txq can send frame to device

 *

 * @hw: pointer obtained from ieee80211_alloc_hw()

 * @txq: pointer obtained from station or virtual interface

 *

 * Return true if the AQL's airtime limit has not been reached and the txq can

 * continue to send more packets to the device. Otherwise return false.

 */

bool

ieee80211_txq_airtime_check(struct ieee80211_hw *hw, struct ieee80211_txq *txq);



/**

 * ieee80211_iter_keys - iterate keys programmed into the device

 * @hw: pointer obtained from ieee80211_alloc_hw()

net/mac80211/debugfs.c

+85 −0
Original line number Diff line number Diff line
@@ -150,6 +150,87 @@ static const struct file_operations aqm_ops = { 
	.llseek = default_llseek,

};



static ssize_t aql_txq_limit_read(struct file *file,

				  char __user *user_buf,

				  size_t count,

				  loff_t *ppos)

{

	struct ieee80211_local *local = file->private_data;

	char buf[400];

	int len = 0;



	len = scnprintf(buf, sizeof(buf),

			"AC	AQL limit low	AQL limit high\n"

			"VO	%u		%u\n"

			"VI	%u		%u\n"

			"BE	%u		%u\n"

			"BK	%u		%u\n",

			local->aql_txq_limit_low[IEEE80211_AC_VO],

			local->aql_txq_limit_high[IEEE80211_AC_VO],

			local->aql_txq_limit_low[IEEE80211_AC_VI],

			local->aql_txq_limit_high[IEEE80211_AC_VI],

			local->aql_txq_limit_low[IEEE80211_AC_BE],

			local->aql_txq_limit_high[IEEE80211_AC_BE],

			local->aql_txq_limit_low[IEEE80211_AC_BK],

			local->aql_txq_limit_high[IEEE80211_AC_BK]);

	return simple_read_from_buffer(user_buf, count, ppos,

				       buf, len);

}



static ssize_t aql_txq_limit_write(struct file *file,

				   const char __user *user_buf,

				   size_t count,

				   loff_t *ppos)

{

	struct ieee80211_local *local = file->private_data;

	char buf[100];

	size_t len;

	u32 ac, q_limit_low, q_limit_high, q_limit_low_old, q_limit_high_old;

	struct sta_info *sta;



	if (count > sizeof(buf))

		return -EINVAL;



	if (copy_from_user(buf, user_buf, count))

		return -EFAULT;



	buf[sizeof(buf) - 1] = 0;

	len = strlen(buf);

	if (len > 0 && buf[len - 1] == '\n')

		buf[len - 1] = 0;



	if (sscanf(buf, "%u %u %u", &ac, &q_limit_low, &q_limit_high) != 3)

		return -EINVAL;



	if (ac >= IEEE80211_NUM_ACS)

		return -EINVAL;



	q_limit_low_old = local->aql_txq_limit_low[ac];

	q_limit_high_old = local->aql_txq_limit_high[ac];



	local->aql_txq_limit_low[ac] = q_limit_low;

	local->aql_txq_limit_high[ac] = q_limit_high;



	mutex_lock(&local->sta_mtx);

	list_for_each_entry(sta, &local->sta_list, list) {

		/* If a sta has customized queue limits, keep it */

		if (sta->airtime[ac].aql_limit_low == q_limit_low_old &&

		    sta->airtime[ac].aql_limit_high == q_limit_high_old) {

			sta->airtime[ac].aql_limit_low = q_limit_low;

			sta->airtime[ac].aql_limit_high = q_limit_high;

		}

	}

	mutex_unlock(&local->sta_mtx);

	return count;

}



static const struct file_operations aql_txq_limit_ops = {

	.write = aql_txq_limit_write,

	.read = aql_txq_limit_read,

	.open = simple_open,

	.llseek = default_llseek,

};



static ssize_t force_tx_status_read(struct file *file,

				    char __user *user_buf,

				    size_t count,
@@ -444,6 +525,10 @@ void debugfs_hw_add(struct ieee80211_local *local) 
	debugfs_create_u16("airtime_flags", 0600,

			   phyd, &local->airtime_flags);



	DEBUGFS_ADD(aql_txq_limit);

	debugfs_create_u32("aql_threshold", 0600,

			   phyd, &local->aql_threshold);



	statsd = debugfs_create_dir("statistics", phyd);



	/* if the dir failed, don't put all the other things into the root! */

net/mac80211/debugfs_sta.c

+33 −10
Original line number Diff line number Diff line
@@ -197,10 +197,12 @@ static ssize_t sta_airtime_read(struct file *file, char __user *userbuf, 
{

	struct sta_info *sta = file->private_data;

	struct ieee80211_local *local = sta->sdata->local;

	size_t bufsz = 200;

	size_t bufsz = 400;

	char *buf = kzalloc(bufsz, GFP_KERNEL), *p = buf;

	u64 rx_airtime = 0, tx_airtime = 0;

	s64 deficit[IEEE80211_NUM_ACS];

	u32 q_depth[IEEE80211_NUM_ACS];

	u32 q_limit_l[IEEE80211_NUM_ACS], q_limit_h[IEEE80211_NUM_ACS];

	ssize_t rv;

	int ac;
@@ -212,19 +214,22 @@ static ssize_t sta_airtime_read(struct file *file, char __user *userbuf, 
		rx_airtime += sta->airtime[ac].rx_airtime;

		tx_airtime += sta->airtime[ac].tx_airtime;

		deficit[ac] = sta->airtime[ac].deficit;

		q_limit_l[ac] = sta->airtime[ac].aql_limit_low;

		q_limit_h[ac] = sta->airtime[ac].aql_limit_high;

		spin_unlock_bh(&local->active_txq_lock[ac]);

		q_depth[ac] = atomic_read(&sta->airtime[ac].aql_tx_pending);

	}



	p += scnprintf(p, bufsz + buf - p,

		"RX: %llu us\nTX: %llu us\nWeight: %u\n"

		"Deficit: VO: %lld us VI: %lld us BE: %lld us BK: %lld us\n",

		rx_airtime,

		tx_airtime,

		sta->airtime_weight,

		deficit[0],

		deficit[1],

		deficit[2],

		deficit[3]);

		"Deficit: VO: %lld us VI: %lld us BE: %lld us BK: %lld us\n"

		"Q depth: VO: %u us VI: %u us BE: %u us BK: %u us\n"

		"Q limit[low/high]: VO: %u/%u VI: %u/%u BE: %u/%u BK: %u/%u\n",

		rx_airtime, tx_airtime, sta->airtime_weight,

		deficit[0], deficit[1], deficit[2], deficit[3],

		q_depth[0], q_depth[1], q_depth[2], q_depth[3],

		q_limit_l[0], q_limit_h[0], q_limit_l[1], q_limit_h[1],

		q_limit_l[2], q_limit_h[2], q_limit_l[3], q_limit_h[3]),



	rv = simple_read_from_buffer(userbuf, count, ppos, buf, p - buf);

	kfree(buf);
@@ -236,7 +241,25 @@ static ssize_t sta_airtime_write(struct file *file, const char __user *userbuf, 
{

	struct sta_info *sta = file->private_data;

	struct ieee80211_local *local = sta->sdata->local;

	int ac;

	u32 ac, q_limit_l, q_limit_h;

	char _buf[100] = {}, *buf = _buf;



	if (count > sizeof(_buf))

		return -EINVAL;



	if (copy_from_user(buf, userbuf, count))

		return -EFAULT;



	buf[sizeof(_buf) - 1] = '\0';

	if (sscanf(buf, "queue limit %u %u %u", &ac, &q_limit_l, &q_limit_h)

	    != 3)

		return -EINVAL;



	if (ac >= IEEE80211_NUM_ACS)

		return -EINVAL;



	sta->airtime[ac].aql_limit_low = q_limit_l;

	sta->airtime[ac].aql_limit_high = q_limit_h;



	for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {

		spin_lock_bh(&local->active_txq_lock[ac]);

net/mac80211/ieee80211_i.h

+4 −0
Original line number Diff line number Diff line
@@ -1142,6 +1142,10 @@ struct ieee80211_local { 
	u16 schedule_round[IEEE80211_NUM_ACS];



	u16 airtime_flags;

	u32 aql_txq_limit_low[IEEE80211_NUM_ACS];

	u32 aql_txq_limit_high[IEEE80211_NUM_ACS];

	u32 aql_threshold;

	atomic_t aql_total_pending_airtime;



	const struct ieee80211_ops *ops;

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