linux-kernel - Re: [RFC PATCH 1/1] mac80211: use AQL airtime for expected throughput.

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Message-ID: <87r14hoox8.fsf@toke.dk>
Date:   Wed, 25 May 2022 13:02:43 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Baligh Gasmi <gasmibal@...il.com>,
        Johannes Berg <johannes@...solutions.net>
Cc:     Baligh Gasmi <gasmibal@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "open list:MAC80211" <linux-wireless@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/1] mac80211: use AQL airtime for expected throughput.

Baligh Gasmi <gasmibal@...il.com> writes:

> Since the integration of AQL, packet TX airtime estimation is
> calculated and counted to be used for the dequeue limit.
>
> Use this estimated airtime to compute expected throughput for
> each station.
>
> It will be a generic mac80211 implementation. If the driver has
> get_expected_throughput implementation, it will be used instead.
>
> Useful for L2 routing protocols, like B.A.T.M.A.N.
>
> Signed-off-by: Baligh Gasmi <gasmibal@...il.com>
> ---
>  net/mac80211/driver-ops.h |  2 ++
>  net/mac80211/sta_info.h   |  2 ++
>  net/mac80211/status.c     | 22 ++++++++++++++++++++++
>  net/mac80211/tx.c         |  3 ++-
>  4 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/net/mac80211/driver-ops.h b/net/mac80211/driver-ops.h
> index 4e2fc1a08681..4331b79647fa 100644
> --- a/net/mac80211/driver-ops.h
> +++ b/net/mac80211/driver-ops.h
> @@ -1142,6 +1142,8 @@ static inline u32 drv_get_expected_throughput(struct ieee80211_local *local,
>  	trace_drv_get_expected_throughput(&sta->sta);
>  	if (local->ops->get_expected_throughput && sta->uploaded)
>  		ret = local->ops->get_expected_throughput(&local->hw, &sta->sta);
> +	else
> +		ret = ewma_avg_est_tp_read(&sta->status_stats.avg_est_tp);
>  	trace_drv_return_u32(local, ret);
>  
>  	return ret;
> diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
> index 379fd367197f..fe60be4c671d 100644
> --- a/net/mac80211/sta_info.h
> +++ b/net/mac80211/sta_info.h
> @@ -123,6 +123,7 @@ enum ieee80211_sta_info_flags {
>  #define HT_AGG_STATE_STOP_CB		7
>  #define HT_AGG_STATE_SENT_ADDBA		8
>  
> +DECLARE_EWMA(avg_est_tp, 8, 16)
>  DECLARE_EWMA(avg_signal, 10, 8)
>  enum ieee80211_agg_stop_reason {
>  	AGG_STOP_DECLINED,
> @@ -641,6 +642,7 @@ struct sta_info {
>  		s8 last_ack_signal;
>  		bool ack_signal_filled;
>  		struct ewma_avg_signal avg_ack_signal;
> +		struct ewma_avg_est_tp avg_est_tp;
>  	} status_stats;
>  
>  	/* Updated from TX path only, no locking requirements */
> diff --git a/net/mac80211/status.c b/net/mac80211/status.c
> index e81e8a5bb774..647ade3719f5 100644
> --- a/net/mac80211/status.c
> +++ b/net/mac80211/status.c
> @@ -1145,6 +1145,28 @@ void ieee80211_tx_status_ext(struct ieee80211_hw *hw,
>  			sta->status_stats.retry_failed++;
>  		sta->status_stats.retry_count += retry_count;
>  
> +		if (skb && tx_time_est) {

Shouldn't this be conditioned on actually being used (i.e., existence of
get_expected_throughput op? Also maybe pull it out into its own function
to make it clear what it's doing...

> +			/* max average packet size */
> +			size_t pkt_size = skb->len > 1024 ? 1024 : skb->len;
> +
> +			if (acked) {
> +				/* ACK packet size */
> +				pkt_size += 14;
> +				/* SIFS x 2 */
> +				tx_time_est += 2 * 2;
> +			}
> +
> +			/* Backoff average x retries */
> +			tx_time_est += retry_count ? retry_count * 2 : 2;
> +
> +			/* failed tx */
> +			if (!acked && !noack_success)
> +				pkt_size = 0;
> +
> +			ewma_avg_est_tp_add(&sta->status_stats.avg_est_tp,
> +					    ((pkt_size * 8) * 1000) / tx_time_est);

Could we avoid adding this division in the fast path?

> +		}
> +
>  		if (ieee80211_hw_check(&local->hw, REPORTS_TX_ACK_STATUS)) {
>  			if (sdata->vif.type == NL80211_IFTYPE_STATION &&
>  			    skb && !(info->flags & IEEE80211_TX_CTL_HW_80211_ENCAP))
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index b6b20f38de0e..d866a721690d 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -3793,7 +3793,8 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
>  	IEEE80211_SKB_CB(skb)->control.vif = vif;
>  
>  	if (vif &&
> -	    wiphy_ext_feature_isset(local->hw.wiphy, NL80211_EXT_FEATURE_AQL)) {
> +	    (!local->ops->get_expected_throughput ||
> +	    wiphy_ext_feature_isset(local->hw.wiphy, NL80211_EXT_FEATURE_AQL))) {

This implicitly enables AQL for every driver that doesn't set
get_expected_throughput, no? That is probably not a good idea...

-Toke