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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 0/1] Bluetooth: Prioritize sco traffic on slow interfaces
Date:   Thu, 12 Mar 2020 11:10:54 -0700
Message-Id: <20200312181055.94038-1-abhishekpandit@chromium.org>
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Sender: linux-bluetooth-owner@vger.kernel.org
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Hi linux-bluetooth,

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.
There were no discernible slowdowns caused by this change.

Thanks
Abhishek


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

 include/net/bluetooth/hci_core.h |  1 +
 net/bluetooth/hci_core.c         | 91 +++++++++++++++++++++++++-------
 2 files changed, 73 insertions(+), 19 deletions(-)

-- 
2.25.1.481.gfbce0eb801-goog