Kan Yan <kyan@xxxxxxxxxx> writes:
> 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: Kan Yan <kyan@xxxxxxxxxx>
> [ Toke: Keep API to set pending airtime internal, fix nits in commit msg ]
> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Thanks for the update! A few comments below. I'll also send you and
updated version of my patch following this one, with fixes for Johannes'
comments. You can include that in your next version...
> ---
> include/net/cfg80211.h | 7 ++++
> include/net/mac80211.h | 12 ++++++
> net/mac80211/debugfs.c | 78 ++++++++++++++++++++++++++++++++++++++
> net/mac80211/debugfs_sta.c | 43 ++++++++++++++++-----
> net/mac80211/ieee80211_i.h | 4 ++
> net/mac80211/main.c | 10 ++++-
> net/mac80211/sta_info.c | 40 +++++++++++++++++++
> net/mac80211/sta_info.h | 8 ++++
> net/mac80211/tx.c | 47 +++++++++++++++++++++--
> 9 files changed, 235 insertions(+), 14 deletions(-)
>
> diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
> index 4ab2c49423dc..15f9f04de149 100644
> --- a/include/net/cfg80211.h
> +++ b/include/net/cfg80211.h
> @@ -2602,6 +2602,13 @@ 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 4000
> +#define IEEE80211_DEFAULT_AQL_TXQ_LIMIT_H 8000
> +
> +/* The per interface airtime threshold to switch to lower queue limit */
> +#define IEEE80211_AQL_THRESHOLD 24000
> +
> /**
> * struct cfg80211_pmksa - PMK Security Association
> *
> diff --git a/include/net/mac80211.h b/include/net/mac80211.h
> index 4319596ef472..269be699e89c 100644
> --- a/include/net/mac80211.h
> +++ b/include/net/mac80211.h
> @@ -5558,6 +5558,18 @@ 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()
> diff --git a/net/mac80211/debugfs.c b/net/mac80211/debugfs.c
> index 568b3b276931..d77ea0e51c1d 100644
> --- a/net/mac80211/debugfs.c
> +++ b/net/mac80211/debugfs.c
> @@ -148,6 +148,80 @@ 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;
> + 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;
> +
> + 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) {
> + sta->airtime[ac].aql_limit_low = q_limit_low;
> + sta->airtime[ac].aql_limit_high = q_limit_high;
> + }
Why is this setting sta and device limits to the same value?
Also, are you sure we won't risk write tearing when writing 32-bit
values without locking on some architectures?
> + 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,
> @@ -441,6 +515,10 @@ 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! */
> diff --git a/net/mac80211/debugfs_sta.c b/net/mac80211/debugfs_sta.c
> index c8ad20c28c43..0185e6e5e5d1 100644
> --- a/net/mac80211/debugfs_sta.c
> +++ b/net/mac80211/debugfs_sta.c
> @@ -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;
Same concern as above re: unprotected writes.
> for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
> spin_lock_bh(&local->active_txq_lock[ac]);
> diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
> index 225ea4e3cd76..ad15b3be8bb3 100644
> --- a/net/mac80211/ieee80211_i.h
> +++ b/net/mac80211/ieee80211_i.h
> @@ -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;
>
> diff --git a/net/mac80211/main.c b/net/mac80211/main.c
> index aba094b4ccfc..071ea92a3748 100644
> --- a/net/mac80211/main.c
> +++ b/net/mac80211/main.c
> @@ -667,8 +667,16 @@ struct ieee80211_hw *ieee80211_alloc_hw_nm(size_t priv_data_len,
> for (i = 0; i < IEEE80211_NUM_ACS; i++) {
> INIT_LIST_HEAD(&local->active_txqs[i]);
> spin_lock_init(&local->active_txq_lock[i]);
> + local->aql_txq_limit_low[i] = IEEE80211_DEFAULT_AQL_TXQ_LIMIT_L;
> + local->aql_txq_limit_high[i] =
> + IEEE80211_DEFAULT_AQL_TXQ_LIMIT_H;
> }
> - local->airtime_flags = AIRTIME_USE_TX | AIRTIME_USE_RX;
> +
> + local->airtime_flags = AIRTIME_USE_TX |
> + AIRTIME_USE_RX |
> + AIRTIME_USE_AQL;
> + local->aql_threshold = IEEE80211_AQL_THRESHOLD;
> + atomic_set(&local->aql_total_pending_airtime, 0);
>
> INIT_LIST_HEAD(&local->chanctx_list);
> mutex_init(&local->chanctx_mtx);
> diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
> index bd11fef2139f..a76e935a543a 100644
> --- a/net/mac80211/sta_info.c
> +++ b/net/mac80211/sta_info.c
> @@ -396,6 +396,9 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
> skb_queue_head_init(&sta->ps_tx_buf[i]);
> skb_queue_head_init(&sta->tx_filtered[i]);
> sta->airtime[i].deficit = sta->airtime_weight;
> + atomic_set(&sta->airtime[i].aql_tx_pending, 0);
> + sta->airtime[i].aql_limit_low = local->aql_txq_limit_low[i];
> + sta->airtime[i].aql_limit_high = local->aql_txq_limit_high[i];
> }
>
> for (i = 0; i < IEEE80211_NUM_TIDS; i++)
> @@ -1893,6 +1896,43 @@ void ieee80211_sta_register_airtime(struct ieee80211_sta *pubsta, u8 tid,
> }
> EXPORT_SYMBOL(ieee80211_sta_register_airtime);
>
> +void ieee80211_sta_update_pending_airtime(struct ieee80211_local *local,
> + struct sta_info *sta, u8 ac,
> + u16 tx_airtime, bool tx_completed)
> +{
> + if (!tx_completed) {
> + if (sta)
> + atomic_add(tx_airtime,
> + &sta->airtime[ac].aql_tx_pending);
> +
> + atomic_add(tx_airtime, &local->aql_total_pending_airtime);
> + return;
> + }
> +
> + if (sta) {
> + if (WARN_ONCE(atomic_read(&sta->airtime[ac].aql_tx_pending) <
> + tx_airtime,
> + "STA %pM AC %d txq pending airtime underflow: %u, %u",
> + sta->addr, ac,
> + atomic_read(&sta->airtime[ac].aql_tx_pending),
> + tx_airtime))
> + atomic_set(&sta->airtime[ac].aql_tx_pending, 0);
I don't think this is right; another thread could do atomic_inc()
between the atomic_read() and atomic_set() here, in which case this
would clobber the other value.
I think to get this right the logic would need to be something like
this:
retry:
old = atomic_read(&sta->airtime[ac].aql_tx_pending);
if (warn_once(tx_airtime > old))
new = 0;
else
new = old - tx_airtime;
if (atomic_cmpxchg(&sta->airtime[ac].aql_tx_pending, old, new) != old)
goto retry;
(or use an equivalent do/while).
-Toke
