Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753457AbcLJQzU (ORCPT ); Sat, 10 Dec 2016 11:55:20 -0500 Received: from mail.savoirfairelinux.com ([208.88.110.44]:49508 "EHLO mail.savoirfairelinux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753067AbcLJQzT (ORCPT ); Sat, 10 Dec 2016 11:55:19 -0500 From: Vivien Didelot To: Nikita Yushchenko , Fugang Duan , "David S. Miller" , Troy Kisky , Florian Fainelli , Andrew Lunn , Eric Nelson , Philippe Reynes , Johannes Berg , netdev@vger.kernel.org Cc: Chris Healy , Fabio Estevam , linux-kernel@vger.kernel.org, Nikita Yushchenko Subject: Re: [PATCH/RFC net-next] net: fec: allow "mini jumbo" frames In-Reply-To: <1481275255-7650-1-git-send-email-nikita.yoush@cogentembedded.com> References: <1481275255-7650-1-git-send-email-nikita.yoush@cogentembedded.com> Date: Sat, 10 Dec 2016 11:55:11 -0500 Message-ID: <87lgvn3es0.fsf@weeman.i-did-not-set--mail-host-address--so-tickle-me> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1217 Lines: 37 Hi Nikita, Nikita Yushchenko writes: > This adds support for MTU slightly larger than default, on modern > FEC flavours. > > Currently FEC driver uses single hardware Rx buffer per frame. On most > FEC flavours, size of single buffer is limited by 11-bit field, and > has to be multiple of 64 (in the worst case). Thus maximum usable Rx > buffer size is 1984 bytes. > > Of those: > - 2 bytes are used for IP header alignment, > - 14 bytes are used by ethhdr, > - up to 8 bytes are needed for VLAN and/or DSA tags, > - 4 bytes are needed for CRC. > > Thus maximum MTU possible within current RX architecture is 1956. > > This patch allows exactly that. For further increase, Rx architecture > change is needed. > > Use of MTU=1956 gives about 1.5% throughput improvement between two Vybrid > boards, compared to default MTU=1500. > > Signed-off-by: Nikita Yushchenko For what it's worth, I have tested your patch on my ZII Rev B boards (see vf610-zii-dev-rev-b.dts) which have a FEC as the master net device of their DSA trees. They still work as expected. Tested-by: Vivien Didelot Thanks, Vivien