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Date: Wed, 25 May 2022 14:14:54 +0200
From: Baligh GASMI <gasmibal@...il.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
Cc: Johannes Berg <johannes@...solutions.net>,
"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.
> > 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...
It's already the case I think, since the tx_time_est is not-zero only
when actually an estimated time is set.
A dedicated function seems good for me, for clarity, yes.
>
> > + /* 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?
Maybe we can use the do_div() macro for optimization, I don't see how
we can avoid it.
>
> > + }
> > +
> > 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...
No, AQL will be disabled if it's already the case, according to the
NL80211_EXT_FEATURE_AQL, only airtime estimation will be activated
with this diff. The function ieee80211_sta_update_pending_airtime() is
already checking for NL80211_EXT_FEATURE_AQL.
>
> -Toke
>
Back to the base idea, what do you think about it, can it be a good
road to take ?
Other factors can be added progressively to better estimate the throughput...
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