On 2019-04-11 19:24, Toke Høiland-Jørgensen wrote:
Yibo Zhao <yiboz@xxxxxxxxxxxxxx> writes:On 2019-04-10 18:40, Toke Høiland-Jørgensen wrote:Yibo Zhao <yiboz@xxxxxxxxxxxxxx> writes:On 2019-04-10 04:41, Toke Høiland-Jørgensen wrote:Yibo Zhao <yiboz@xxxxxxxxxxxxxx> writes:On 2019-04-04 16:31, Toke Høiland-Jørgensen wrote:Yibo Zhao <yiboz@xxxxxxxxxxxxxx> writes:On 2019-02-16 01:05, Toke Høiland-Jørgensen wrote:This switches the airtime scheduler in mac80211 to use a virtualtime-basedscheduler instead of the round-robin scheduler used before. Thishas 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 needto maintain an rbtree of TXQs sorted by virtual time. This meansthat ieee80211_register_airtime() becomes O(logN) in the number of currently scheduled TXQs. However, hopefully this number rarely grows too big (it'sonly TXQs currently backlogged, not all associated stations), soit shouldn't be too big of an issue. @@ -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;
Hi Toke,I was porting this version of ATF design to my ath10k platform and found my old kernel version not supporting 64bit division. I'm wondering if it is necessary to use u64 for airtime and weight_sum here though I can find a solution for it. I think u32 might be enough. For airtime, u32_max / 256 = 7182219 us(718 ms). As for weight_sum, u32_max / 8092 us = 130490, meaning we can support more than 130000 nodes with airtime weight 8092 us.
Another finding was when I configured two 11ac STAs with different airtime weight, such as 256 and 1024 meaning ratio is 1:4, the throughput ratio was not roughly matching the ratio. Could you please share your results? I am not sure if it is due to platform difference.
Hi Toke, Please ignore the previous two broken emails regarding this new proposal from me.It looks like local->airtime_v_t acts like a Tx criteria. Only the stations with less airtime than that are valid for Tx. That meansthereare situations, like 50 clients, that some of the stations can beused to Tx when putting next_txq in the loop. Am I right?I'm not sure what you mean here. Are you referring to the case where newstations appear with a very low (zero) airtime_v_t? That is handledwhen the station is enqueued.Hi Toke, Sorry for the confusion. I am not referring to the case that you mentioned though it can be solved by your subtle design, max(local vt, sta vt). :-) Actually, my concern is situation about putting next_txq in the loop. Let me explain a little more and see below.@@ -3640,126 +3638,191 @@ EXPORT_SYMBOL(ieee80211_tx_dequeue);struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw,u8 ac) { struct ieee80211_local *local = hw_to_local(hw); + struct rb_node *node = local->schedule_pos[ac]; struct txq_info *txqi = NULL; + bool first = false; lockdep_assert_held(&local->active_txq_lock[ac]); - begin: - txqi = list_first_entry_or_null(&local->active_txqs[ac], - struct txq_info, - schedule_order); - if (!txqi) + if (!node) { + node = rb_first_cached(&local->active_txqs[ac]); + first = true; + } else + node = rb_next(node);Consider below piece of code from ath10k_mac_schedule_txq: ieee80211_txq_schedule_start(hw, ac); while ((txq = ieee80211_next_txq(hw, ac))) { while (ath10k_mac_tx_can_push(hw, txq)) { ret = ath10k_mac_tx_push_txq(hw, txq); if (ret < 0) break; } ieee80211_return_txq(hw, txq); ath10k_htt_tx_txq_update(hw, txq); if (ret == -EBUSY) break; } ieee80211_txq_schedule_end(hw, ac);If my understanding is right, local->schedule_pos is used to recordthe last scheduled node and used for traversal rbtree for valid txq. Thereis chance that an empty txq is feeded to return_txq and got removedfromrbtree. The empty txq will always be the rb_first node. Then in thefollowing next_txq, local->schedule_pos becomes meaningless since its rb_next will return NULL and the loop break. Only rb_first get dequeued during this loop. if (!node || RB_EMPTY_NODE(node)) { node = rb_first_cached(&local->active_txqs[ac]); first = true; } else node = rb_next(node);Ah, I see what you mean. Yes, that would indeed be a problem - nice catch! :)How about this? The nodes on the rbtree will be dequeued and removedfrom rbtree one by one until HW is busy. Please note local vt and sta vt will not be updated since txq lock is held during this time.Insertion and removal from the rbtree are relatively expensive, so I'drather not do that for every txq. I think a better way to solve thisis to just defer the actual removal from the tree until ieee80211_txq_schedule_end()... Will fix that when I submit this again.Do you mean we keep the empty txqs in the rbtree until loop finishes and remove them in ieee80211_txq_schedule_end(may be put return_txq in it)?If it is the case, I suppose a list is needed to store the empty txqsso as to dequeue them in ieee80211_txq_schedule_end.Yeah, return_txq() would just put "to be removed" TXQs on a list, and schedule_end() would do the actual removal (after checking whether a new packet showed up in the meantime).SGTMAnd one more thing,+ if (sta->airtime[ac].v_t > local->airtime_v_t[ac]) {+ if (first) + local->airtime_v_t[ac] = sta->airtime[ac].v_t; + else + return NULL;As local->airtime_v_t will not be updated during loop, we don't need to return NULL.Yes we do; this is actually the break condition. I.e., stations whose virtual time are higher than the global time (in local->airtime_v_t) are not allowed to transmit. And since we are traversing them in order, when we find the first such station, we are done and can break out of the scheduling loop entirely (which is what we do by returning NULL). The other branch in the inner if() is just for the case where no stations are currently eligible to transmit according to this rule; here we don't want to stall, so we advance the global timer so the first station becomes eligible...Yes，the inner if() make sure first node always get scheduled no matter its vt. To detail my concern, let's assume only two nodes in the tree and empty nodes will be in tree until schedule_end(). In the loop and in case hw is not busy, ath10k will drain every node next_txq returned before asking for another txq again. Then as we are traversing to next rb node, it is highly possible the second node is not allowed to transmit since the global time has not been updated yet as the active txq lock is held. At this time, only second node on the tree has data and hw is capable of sending more data. I don't think the second node is not valid for transmission in this situation. With more nodes in the tree in this situation, I think same thing happens that all nodes except the first node are not allowed to transmit since none of their vts are less than the global time which is not updated in time. The loop breaks when we are checking the second node.Yeah, in many cases we will end up throttling all but the first (couple of) node(s). This is by design; otherwise we can't ensure fairness. As long as we are making forward progress that is fine, though... -Toke
-- Yibo
