Re: [PATCH v3 1/1] Bluetooth: Prioritize SCO traffic

[Abhishek Pandit-Subedi]

Hi Marcel,

Reminder to review this patch.

Thanks,
Abhishek

On Mon, Mar 23, 2020 at 12:45 PM Abhishek Pandit-Subedi
<abhishekpandit@xxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxx>
> ---
>
> Changes in v3:
> * Removed hci_sched_sync
>
> 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 | 106 +++++++++++++++++++++------------------
>  1 file changed, 57 insertions(+), 49 deletions(-)
>
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index dbd2ad3a26ed..9e5d7662a047 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -4239,6 +4239,54 @@ 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, &quote))) {
> +               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,
> +                                                    &quote))) {
> +               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_acl_pkt(struct hci_dev *hdev)
>  {
>         unsigned int cnt = hdev->acl_cnt;
> @@ -4270,6 +4318,10 @@ 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_sco(hdev);
> +                       hci_sched_esco(hdev);
>                 }
>         }
>
> @@ -4354,54 +4406,6 @@ 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, &quote))) {
> -               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,
> -                                                    &quote))) {
> -               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 +4440,10 @@ static void hci_sched_le(struct hci_dev *hdev)
>                         cnt--;
>                         chan->sent++;
>                         chan->conn->sent++;
> +
> +                       /* Send pending SCO packets right away */
> +                       hci_sched_sco(hdev);
> +                       hci_sched_esco(hdev);
>                 }
>         }
>
> @@ -4458,9 +4466,9 @@ 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_acl(hdev);
>                 hci_sched_sco(hdev);
>                 hci_sched_esco(hdev);
> +               hci_sched_acl(hdev);
>                 hci_sched_le(hdev);
>         }
>
> --
> 2.25.1.696.g5e7596f4ac-goog
>