From: Yibo Zhao <yiboz@codeaurora.org>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: make-wifi-fast@lists.bufferbloat.net,
linux-wireless@vger.kernel.org, Felix Fietkau <nbd@nbd.name>,
Rajkumar Manoharan <rmanohar@codeaurora.org>,
Kan Yan <kyan@google.com>,
linux-wireless-owner@vger.kernel.org
Subject: Re: [RFC/RFT] mac80211: Switch to a virtual time-based airtime scheduler
Date: Wed, 10 Apr 2019 14:35:39 +0800 [thread overview]
Message-ID: <89d32174b282006c8d4e7614657171be@codeaurora.org> (raw)
In-Reply-To: <877ec2ykrh.fsf@toke.dk>
On 2019-04-10 04:41, Toke Høiland-Jørgensen wrote:
> Yibo Zhao <yiboz@codeaurora.org> writes:
>
>> On 2019-04-04 16:31, Toke Høiland-Jørgensen wrote:
>>> Yibo Zhao <yiboz@codeaurora.org> 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.
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 txqs so
as to dequeue them in ieee80211_txq_schedule_end.
And 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.
>
> -Toke
--
Yibo
next prev parent reply other threads:[~2019-04-10 6:35 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-15 17:05 [RFC/RFT] mac80211: Switch to a virtual time-based airtime scheduler Toke Høiland-Jørgensen
2019-02-15 19:44 ` [Make-wifi-fast] " Dave Taht
2019-03-05 15:45 ` Toke Høiland-Jørgensen
2019-03-06 23:09 ` Rajkumar Manoharan
2019-03-07 9:46 ` Toke Høiland-Jørgensen
2019-03-07 14:27 ` Felix Fietkau
2019-03-08 11:05 ` Toke Høiland-Jørgensen
2019-03-08 18:16 ` Felix Fietkau
2019-03-08 19:06 ` Toke Høiland-Jørgensen
2019-04-04 4:41 ` Yibo Zhao
2019-04-04 4:43 ` Yibo Zhao
2019-04-04 5:00 ` Yibo Zhao
2019-04-04 8:31 ` Toke Høiland-Jørgensen
2019-04-04 8:36 ` [Make-wifi-fast] " Dave Taht
2019-04-04 8:50 ` Toke Høiland-Jørgensen
2019-04-09 13:25 ` Yibo Zhao
2019-04-09 20:41 ` Toke Høiland-Jørgensen
2019-04-10 6:35 ` Yibo Zhao [this message]
2019-04-10 10:40 ` Toke Høiland-Jørgensen
2019-04-11 3:12 ` Yibo Zhao
2019-04-11 11:24 ` Toke Høiland-Jørgensen
2019-04-12 6:34 ` Yibo Zhao
2019-04-19 15:05 ` Yibo Zhao
2019-04-20 21:15 ` Toke Høiland-Jørgensen
2019-04-30 9:45 ` Yibo Zhao
2019-04-30 10:39 ` Toke Høiland-Jørgensen
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