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Date: Mon, 23 Mar 2020 19:58:27 +0100
From: Marcel Holtmann <marcel@...tmann.org>
To: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
Cc: Bluetooth Kernel Mailing List <linux-bluetooth@...r.kernel.org>,
chromeos-bluetooth-upstreaming@...omium.org,
"David S. Miller" <davem@...emloft.net>,
Johan Hedberg <johan.hedberg@...il.com>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH v2 1/1] Bluetooth: Prioritize SCO traffic
Hi Abhishek,
> When scheduling TX packets, send all SCO/eSCO packets first, check for
> pending SCO/eSCO packets after every ACL/LE packet and send them if any
> are pending. This is done to make sure that we can meet SCO deadlines
> on slow interfaces like UART.
>
> If we were to queue up multiple ACL packets without checking for a SCO
> packet, we might miss the SCO timing. For example:
>
> The time it takes to send a maximum size ACL packet (1024 bytes):
> t = 10/8 * 1024 bytes * 8 bits/byte * 1 packet / baudrate
> where 10/8 is uart overhead due to start/stop bits per byte
>
> Replace t = 3.75ms (SCO deadline), which gives us a baudrate of 2730666.
>
> At a baudrate of 3000000, if we didn't check for SCO packets within 1024
> bytes, we would miss the 3.75ms timing window.
>
> Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
> ---
>
> Changes in v2:
> * Refactor to check for SCO/eSCO after each ACL/LE packet sent
> * Enabled SCO priority all the time and removed the sched_limit variable
>
> net/bluetooth/hci_core.c | 111 +++++++++++++++++++++------------------
> 1 file changed, 61 insertions(+), 50 deletions(-)
>
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index dbd2ad3a26ed..a29177e1a9d0 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -4239,6 +4239,60 @@ static void __check_timeout(struct hci_dev *hdev, unsigned int cnt)
> }
> }
>
> +/* Schedule SCO */
> +static void hci_sched_sco(struct hci_dev *hdev)
> +{
> + struct hci_conn *conn;
> + struct sk_buff *skb;
> + int quote;
> +
> + BT_DBG("%s", hdev->name);
> +
> + if (!hci_conn_num(hdev, SCO_LINK))
> + return;
> +
> + while (hdev->sco_cnt && (conn = hci_low_sent(hdev, SCO_LINK, "e))) {
> + while (quote-- && (skb = skb_dequeue(&conn->data_q))) {
> + BT_DBG("skb %p len %d", skb, skb->len);
> + hci_send_frame(hdev, skb);
> +
> + conn->sent++;
> + if (conn->sent == ~0)
> + conn->sent = 0;
> + }
> + }
> +}
> +
> +static void hci_sched_esco(struct hci_dev *hdev)
> +{
> + struct hci_conn *conn;
> + struct sk_buff *skb;
> + int quote;
> +
> + BT_DBG("%s", hdev->name);
> +
> + if (!hci_conn_num(hdev, ESCO_LINK))
> + return;
> +
> + while (hdev->sco_cnt && (conn = hci_low_sent(hdev, ESCO_LINK,
> + "e))) {
> + while (quote-- && (skb = skb_dequeue(&conn->data_q))) {
> + BT_DBG("skb %p len %d", skb, skb->len);
> + hci_send_frame(hdev, skb);
> +
> + conn->sent++;
> + if (conn->sent == ~0)
> + conn->sent = 0;
> + }
> + }
> +}
> +
> +static void hci_sched_sync(struct hci_dev *hdev)
> +{
> + hci_sched_sco(hdev);
> + hci_sched_esco(hdev);
> +}
> +
scrap this function. It has almost zero benefit.
> static void hci_sched_acl_pkt(struct hci_dev *hdev)
> {
> unsigned int cnt = hdev->acl_cnt;
> @@ -4270,6 +4324,9 @@ static void hci_sched_acl_pkt(struct hci_dev *hdev)
> hdev->acl_cnt--;
> chan->sent++;
> chan->conn->sent++;
> +
> + /* Send pending SCO packets right away */
> + hci_sched_sync(hdev);
hci_sched_esco();
hci_sched_sco();
> }
> }
>
> @@ -4354,54 +4411,6 @@ static void hci_sched_acl(struct hci_dev *hdev)
> }
> }
>
> -/* Schedule SCO */
> -static void hci_sched_sco(struct hci_dev *hdev)
> -{
> - struct hci_conn *conn;
> - struct sk_buff *skb;
> - int quote;
> -
> - BT_DBG("%s", hdev->name);
> -
> - if (!hci_conn_num(hdev, SCO_LINK))
> - return;
> -
> - while (hdev->sco_cnt && (conn = hci_low_sent(hdev, SCO_LINK, "e))) {
> - while (quote-- && (skb = skb_dequeue(&conn->data_q))) {
> - BT_DBG("skb %p len %d", skb, skb->len);
> - hci_send_frame(hdev, skb);
> -
> - conn->sent++;
> - if (conn->sent == ~0)
> - conn->sent = 0;
> - }
> - }
> -}
> -
> -static void hci_sched_esco(struct hci_dev *hdev)
> -{
> - struct hci_conn *conn;
> - struct sk_buff *skb;
> - int quote;
> -
> - BT_DBG("%s", hdev->name);
> -
> - if (!hci_conn_num(hdev, ESCO_LINK))
> - return;
> -
> - while (hdev->sco_cnt && (conn = hci_low_sent(hdev, ESCO_LINK,
> - "e))) {
> - while (quote-- && (skb = skb_dequeue(&conn->data_q))) {
> - BT_DBG("skb %p len %d", skb, skb->len);
> - hci_send_frame(hdev, skb);
> -
> - conn->sent++;
> - if (conn->sent == ~0)
> - conn->sent = 0;
> - }
> - }
> -}
> -
> static void hci_sched_le(struct hci_dev *hdev)
> {
> struct hci_chan *chan;
> @@ -4436,6 +4445,9 @@ static void hci_sched_le(struct hci_dev *hdev)
> cnt--;
> chan->sent++;
> chan->conn->sent++;
> +
> + /* Send pending SCO packets right away */
> + hci_sched_sync(hdev);
Same as above. Just call the two functions.
> }
> }
>
> @@ -4458,9 +4470,8 @@ static void hci_tx_work(struct work_struct *work)
>
> if (!hci_dev_test_flag(hdev, HCI_USER_CHANNEL)) {
> /* Schedule queues and send stuff to HCI driver */
> + hci_sched_sync(hdev);
> hci_sched_acl(hdev);
> - hci_sched_sco(hdev);
> - hci_sched_esco(hdev);
> hci_sched_le(hdev);
I would actually just move _le up after _acl and then keep _sco and _esco at the bottom. The calls here are just for the case there are no ACL nor LE packets.
Regards
Marcel
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