From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ezequiel Garcia Subject: Re: [PATCH] net: mvneta: fix Tx interrupt delay Date: Tue, 02 Dec 2014 14:12:10 -0300 Message-ID: <547DF2EA.2020908@free-electrons.com> References: <20141202071304.GA22512@1wt.eu> <1417522688.5303.35.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org, Maggie Mae Roxas , Thomas Petazzoni , Gregory CLEMENT To: Eric Dumazet , Willy Tarreau Return-path: Received: from down.free-electrons.com ([37.187.137.238]:34180 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754139AbaLBROD (ORCPT ); Tue, 2 Dec 2014 12:14:03 -0500 In-Reply-To: <1417522688.5303.35.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: Eric, On 12/02/2014 09:18 AM, Eric Dumazet wrote: [..] >=20 > I am surprised TCP even worked correctly with this problem. >=20 > I highly suggest BQL for this driver, now this issue is fixed. >=20 Implementing BQL for the mvneta driver was something I wanted to do a while ago, but you explained that these kind drivers (i.e. those with software TSO) didn't need BQL, because the latency that resulted from the ring was too small. Quoting (http://www.spinics.net/lists/netdev/msg284439.html): "" Note that a full size TSO packet (44 or 45 MSS) requires about 88 or 90 descriptors. So I do not think BQL is really needed, because a 512 slots TX ring won= t add a big latency : About 5 ms max. BQL is generally nice for NIC supporting hardware TSO, where a 64KB TSO packet consumes 3 or 4 descriptors. Also note that TCP Small Queues should limit TX ring occupancy of a single bulk flow anyway. "" Maybe I misunderstood something? --=20 Ezequiel Garc=C3=ADa, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com