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 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.
>>>>
>>>> @@ -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,
>>>
>>> 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 means
>>> there
>>> are situations, like 50 clients, that some of the stations can be used
>>> 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
>> new
>> stations appear with a very low (zero) airtime_v_t? That is handled
>> when
>> 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 record the
> last scheduled node and used for traversal rbtree for valid txq. There
> is chance that an empty txq is feeded to return_txq and got removed from
> rbtree. The empty txq will always be the rb_first node. Then in the
> following 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 removed
> from 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'd
rather not do that for every txq. I think a better way to solve this
is to just defer the actual removal from the tree until
ieee80211_txq_schedule_end()... Will fix that when I submit this again.
-Toke
