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From:   Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
To:     marcel@holtmann.org, linux-bluetooth@vger.kernel.org
Cc:     chromeos-bluetooth-upstreaming@chromium.org,
        Abhishek Pandit-Subedi <abhishekpandit@chromium.org>,
        "David S. Miller" <davem@davemloft.net>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH v3 0/1] Bluetooth: Prioritize sco traffic on slow interfaces
Date:   Mon, 23 Mar 2020 12:45:06 -0700
Message-Id: <20200323194507.90944-1-abhishekpandit@chromium.org>
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Hi Marcel,

While investigating supporting Voice over HCI/UART, we discovered that
it is possible for SCO packet deadlines to be missed in some conditions
where large ACL packets are being transferred. For UART, at a baudrate
of 3000000, a single 1024 byte packet will take ~3.4ms to transfer.
Sending two ACL packets of max size would cause us to miss the timing
for SCO (which is 3.75ms) in the worst case.

To mitigate this, we change hci_tx_work to prefer scheduling SCO/eSCO
over ACL/LE and modify the hci_sched_{acl,le} routines so that they will
only send one packet before checking whether a SCO packet is queued. ACL
packets should still get sent at a similar rate (depending on number of
ACL packets supported by controller) since the loop will continue until
there is no more quota left for ACL and LE packets.

To test this patch, I played some music over SCO (open youtube and
a video conference page at the same time) while using an LE keyboard and
mouse.  There were no discernible slowdowns caused by this change.

Thanks
Abhishek

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

Abhishek Pandit-Subedi (1):
  Bluetooth: Prioritize SCO traffic

 net/bluetooth/hci_core.c | 106 +++++++++++++++++++++------------------
 1 file changed, 57 insertions(+), 49 deletions(-)

-- 
2.25.1.696.g5e7596f4ac-goog