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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
To:     Ben Greear <greearb@candelatech.com>,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH] ath10k: Restart xmit queues below low-water mark.
In-Reply-To: <d72dbba0-409f-93d7-5364-bc7ac50288b9@candelatech.com>
References: <20200427145435.13151-1-greearb@candelatech.com> <87h7x3v1tn.fsf@toke.dk> <d72dbba0-409f-93d7-5364-bc7ac50288b9@candelatech.com>
Date:   Tue, 28 Apr 2020 22:39:28 +0200
Message-ID: <87a72vuyyn.fsf@toke.dk>
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Sender: linux-wireless-owner@vger.kernel.org
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Ben Greear <greearb@candelatech.com> writes:

> On 04/28/2020 12:37 PM, Toke H=C3=B8iland-J=C3=B8rgensen wrote:
>> greearb@candelatech.com writes:
>>
>>> From: Ben Greear <greearb@candelatech.com>
>>>
>>> While running tcp upload + download tests with ~200
>>> concurrent TCP streams, 1-2 processes, and 30 station
>>> vdevs, I noticed that the __ieee80211_stop_queue was taking
>>> around 20% of the CPU according to perf-top, which other locking
>>> taking an additional ~15%.
>>>
>>> I believe the issue is that the ath10k driver would unlock the
>>> txqueue when a single frame could be transmitted, instead of
>>> waiting for a low water mark.
>>>
>>> So, this patch adds a low-water mark that is 1/4 of the total
>>> tx buffers allowed.
>>>
>>> This appears to resolve the performance problem that I saw.
>>>
>>> Tested with recent wave-1 ath10k-ct firmware.
>>>
>>> Signed-off-by: Ben Greear <greearb@candelatech.com>
>>> ---
>>>  drivers/net/wireless/ath/ath10k/htt.h    | 1 +
>>>  drivers/net/wireless/ath/ath10k/htt_tx.c | 8 ++++++--
>>>  2 files changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/wireless/ath/ath10k/htt.h b/drivers/net/wirele=
ss/ath/ath10k/htt.h
>>> index 31c4ddbf45cb..b5634781c0dc 100644
>>> --- a/drivers/net/wireless/ath/ath10k/htt.h
>>> +++ b/drivers/net/wireless/ath/ath10k/htt.h
>>> @@ -1941,6 +1941,7 @@ struct ath10k_htt {
>>>
>>>  	u8 target_version_major;
>>>  	u8 target_version_minor;
>>> +	bool needs_unlock;
>>>  	struct completion target_version_received;
>>>  	u8 max_num_amsdu;
>>>  	u8 max_num_ampdu;
>>> diff --git a/drivers/net/wireless/ath/ath10k/htt_tx.c b/drivers/net/wir=
eless/ath/ath10k/htt_tx.c
>>> index 9b3c3b080e92..44795d9a7c0c 100644
>>> --- a/drivers/net/wireless/ath/ath10k/htt_tx.c
>>> +++ b/drivers/net/wireless/ath/ath10k/htt_tx.c
>>> @@ -145,8 +145,10 @@ void ath10k_htt_tx_dec_pending(struct ath10k_htt *=
htt)
>>>  	lockdep_assert_held(&htt->tx_lock);
>>>
>>>  	htt->num_pending_tx--;
>>> -	if (htt->num_pending_tx =3D=3D htt->max_num_pending_tx - 1)
>>> +	if ((htt->num_pending_tx <=3D (htt->max_num_pending_tx / 4)) && htt->=
needs_unlock) {
>>
>> Why /4? Seems a bit arbitrary?
>
> Yes, arbitrary for sure. I figure restart filling the queue when 1/4
> full so that it is unlikely to run dry. Possibly it should restart
> sooner to keep it more full on average?

Theoretically, the "keep the queue at the lowest possible level that
keeps it from underflowing" is what BQL is supposed to do. The diff
below uses the dynamic adjustment bit (from dynamic_queue_limits.h) in
place of num_pending_tx. I've only compile tested it, and I'm a bit
skeptical that it will work right for this, but if anyone wants to give
it a shot, there it is.

BTW, while doing that, I noticed there's a similar arbitrary limit in
ath10k_mac_tx_push_pending() at max_num_pending_tx/2. So if you're going
to keep the arbitrary limit maybe use the same one? :)

> Before my patch, the behaviour would be to try to keep it as full as
> possible, as in restart the queues as soon as a single slot opens up
> in the tx queue.

Yeah, that seems somewhat misguided as well, from a latency perspective,
at least. But I guess that's what we're fixing with AQL. What does the
firmware do with the frames queued within? Do they just go on a FIFO
queue altogether, or something smarter?

-Toke


diff --git a/drivers/net/wireless/ath/ath10k/core.c b/drivers/net/wireless/=
ath/ath10k/core.c
index f26cc6989dad..72771ff38a94 100644
--- a/drivers/net/wireless/ath/ath10k/core.c
+++ b/drivers/net/wireless/ath/ath10k/core.c
@@ -2497,6 +2497,10 @@ static int ath10k_core_init_firmware_features(struct=
 ath10k *ar)
 		return -EINVAL;
 	}
=20
+	dql_init(&ar->htt.dql, HZ);
+	ar->htt.dql.max_limit =3D ar->htt.max_num_pending_tx;
+	ar->htt.dql.min_limit =3D 8;
+
 	if (ar->hw_params.num_peers)
 		ar->max_num_peers =3D ar->hw_params.num_peers;
 	else
diff --git a/drivers/net/wireless/ath/ath10k/htt.h b/drivers/net/wireless/a=
th/ath10k/htt.h
index 4a12564fc30e..19024d063896 100644
--- a/drivers/net/wireless/ath/ath10k/htt.h
+++ b/drivers/net/wireless/ath/ath10k/htt.h
@@ -13,6 +13,7 @@
 #include <linux/dmapool.h>
 #include <linux/hashtable.h>
 #include <linux/kfifo.h>
+#include <linux/dynamic_queue_limits.h>
 #include <net/mac80211.h>
=20
 #include "htc.h"
@@ -1965,8 +1966,8 @@ struct ath10k_htt {
 	/* Protects access to pending_tx, num_pending_tx */
 	spinlock_t tx_lock;
 	int max_num_pending_tx;
-	int num_pending_tx;
 	int num_pending_mgmt_tx;
+	struct dql dql;
 	struct idr pending_tx;
 	wait_queue_head_t empty_tx_wq;
=20
diff --git a/drivers/net/wireless/ath/ath10k/htt_tx.c b/drivers/net/wireles=
s/ath/ath10k/htt_tx.c
index e9d12ea708b6..911a79470bdf 100644
--- a/drivers/net/wireless/ath/ath10k/htt_tx.c
+++ b/drivers/net/wireless/ath/ath10k/htt_tx.c
@@ -144,8 +144,8 @@ void ath10k_htt_tx_dec_pending(struct ath10k_htt *htt)
 {
 	lockdep_assert_held(&htt->tx_lock);
=20
-	htt->num_pending_tx--;
-	if (htt->num_pending_tx =3D=3D htt->max_num_pending_tx - 1)
+	dql_completed(&htt->dql, 1);
+	if (dql_avail(&htt->dql) > 0)
 		ath10k_mac_tx_unlock(htt->ar, ATH10K_TX_PAUSE_Q_FULL);
 }
=20
@@ -153,11 +153,11 @@ int ath10k_htt_tx_inc_pending(struct ath10k_htt *htt)
 {
 	lockdep_assert_held(&htt->tx_lock);
=20
-	if (htt->num_pending_tx >=3D htt->max_num_pending_tx)
+	if (dql_avail(&htt->dql) <=3D 0)
 		return -EBUSY;
=20
-	htt->num_pending_tx++;
-	if (htt->num_pending_tx =3D=3D htt->max_num_pending_tx)
+	dql_queued(&htt->dql, 1);
+	if (dql_avail(&htt->dql) <=3D 0)
 		ath10k_mac_tx_lock(htt->ar, ATH10K_TX_PAUSE_Q_FULL);
=20
 	return 0;
diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/a=
th/ath10k/mac.c
index 2d03b8dd3b8c..1fe251742b0a 100644
--- a/drivers/net/wireless/ath/ath10k/mac.c
+++ b/drivers/net/wireless/ath/ath10k/mac.c
@@ -3998,7 +3998,7 @@ static bool ath10k_mac_tx_can_push(struct ieee80211_h=
w *hw,
 	if (ar->htt.tx_q_state.mode =3D=3D HTT_TX_MODE_SWITCH_PUSH)
 		return true;
=20
-	if (ar->htt.num_pending_tx < ar->htt.tx_q_state.num_push_allowed)
+	if (dql_avail(&ar->htt.dql) < ar->htt.tx_q_state.num_push_allowed)
 		return true;
=20
 	if (artxq->num_fw_queued < artxq->num_push_allowed)
@@ -4159,7 +4159,7 @@ void ath10k_mac_tx_push_pending(struct ath10k *ar)
 	if (ar->htt.tx_q_state.mode !=3D HTT_TX_MODE_SWITCH_PUSH)
 		return;
=20
-	if (ar->htt.num_pending_tx >=3D (ar->htt.max_num_pending_tx / 2))
+	if (dql_avail(&ar->htt.dql) < (ar->htt.dql.limit / 2))
 		return;
=20
 	rcu_read_lock();
@@ -7160,7 +7160,7 @@ void ath10k_mac_wait_tx_complete(struct ath10k *ar)
 			bool empty;
=20
 			spin_lock_bh(&ar->htt.tx_lock);
-			empty =3D (ar->htt.num_pending_tx =3D=3D 0);
+			empty =3D (ar->htt.dql.num_completed =3D=3D ar->htt.dql.num_queued);
 			spin_unlock_bh(&ar->htt.tx_lock);
=20
 			skip =3D (ar->state =3D=3D ATH10K_STATE_WEDGED) ||
diff --git a/drivers/net/wireless/ath/ath10k/txrx.c b/drivers/net/wireless/=
ath/ath10k/txrx.c
index 39abf8b12903..fe7cd53c2bf9 100644
--- a/drivers/net/wireless/ath/ath10k/txrx.c
+++ b/drivers/net/wireless/ath/ath10k/txrx.c
@@ -80,7 +80,7 @@ int ath10k_txrx_tx_unref(struct ath10k_htt *htt,
=20
 	ath10k_htt_tx_free_msdu_id(htt, tx_done->msdu_id);
 	ath10k_htt_tx_dec_pending(htt);
-	if (htt->num_pending_tx =3D=3D 0)
+	if (htt->dql.num_completed =3D=3D htt->dql.num_queued)
 		wake_up(&htt->empty_tx_wq);
 	spin_unlock_bh(&htt->tx_lock);
=20