On 2019-03-08 12:05, Toke Høiland-Jørgensen wrote: > Felix Fietkau <[email protected]> writes: > >> On 2019-02-15 18:05, 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 <[email protected]> >> The approach looks good to me, but I haven't really reviewed it very >> carefully yet. Just some points that I noticed below: > > Cool! > >>> diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c >>> index 11f058987a54..9d01fdd86e2d 100644 >>> --- a/net/mac80211/sta_info.c >>> +++ b/net/mac80211/sta_info.c >>> @@ -389,7 +389,6 @@ struct sta_info *sta_info_alloc(struct >>> ieee80211_sub_if_data *sdata, >>> for (i = 0; i < IEEE80211_NUM_ACS; i++) { >>> skb_queue_head_init(&sta->ps_tx_buf[i]); >>> skb_queue_head_init(&sta->tx_filtered[i]); >>> - sta->airtime[i].deficit = sta->airtime_weight; >>> } >>> >>> for (i = 0; i < IEEE80211_NUM_TIDS; i++) >>> @@ -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; >>> + sta->airtime[ac].v_t += airtime / sta->airtime_weight; >>> + ieee80211_resort_txq(&local->hw, txq); >> These divisions could be a bit expensive, any way to change the >> calculation to avoid them? > > Yeah, given that the denominators are constant from the PoV of the fast > path, we can pre-compute reciprocals and turn these divides into > multiplications. Will incorporate that... Sounds good.
>> I'm a bit worried about this part. Does that mean that vif txqs always >> have priority over sta txqs? > > Yeah, it does. This sort of mirrors what the existing airtime scheduler > does (because VIFs don't have an airtime deficit), but because it's a > round-robin scheduler the effect is less severe as long as there are > stations able to transmit. > > I guess the obvious fix is to start accounting airtime usage for the VIF > as well? We may want to do that in any case, as that would also give > users a convenient way to set policy for multicast traffic. Any > objections to this? I think this is a good idea. - Felix
