Return-Path: Subject: Re: [PATCH 9/9] Bluetooth: Use 3-DH5 payload size for default ERTM max PDU size. From: Marcel Holtmann To: Mat Martineau Cc: linux-bluetooth@vger.kernel.org, gustavo@padovan.org, rshaffer@codeaurora.org, linux-arm-msm@vger.kernel.org In-Reply-To: <1281048867-32630-10-git-send-email-mathewm@codeaurora.org> References: <1281048867-32630-1-git-send-email-mathewm@codeaurora.org> <1281048867-32630-10-git-send-email-mathewm@codeaurora.org> Content-Type: text/plain; charset="UTF-8" Date: Mon, 09 Aug 2010 04:44:06 -0400 Message-ID: <1281343446.12579.193.camel@localhost.localdomain> Mime-Version: 1.0 Sender: linux-bluetooth-owner@vger.kernel.org List-ID: Hi Mat, > The previous value of 672 for L2CAP_DEFAULT_MAX_PDU_SIZE is based on > the default L2CAP MTU. That default MTU is calculated from the size > of two DH5 packets, minus ACL and L2CAP b-frame header overhead. > > ERTM is used with newer basebands that typically support larger 3-DH5 > packets, and i-frames and s-frames have more header overhead. With > clean RF conditions, basebands will typically attempt to use 1021-byte > 3-DH5 packets for maximum throughput. Adjusting for 2 bytes of ACL > headers plus 10 bytes of worst-case L2CAP headers yields 1009 bytes > of payload. > > This PDU size imposes less overhead for header bytes and gives the > baseband the option to choose 3-DH5 packets, but is small enough for > ERTM traffic to interleave well with other L2CAP or SCO data. > 672-byte payloads do not allow the most efficient over-the-air > packet choice, and cannot achieve maximum throughput over BR/EDR. > > Signed-off-by: Mat Martineau > --- > include/net/bluetooth/l2cap.h | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) patch has been applied. Thanks. Regards Marcel