From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35CC0C433E7 for ; Wed, 14 Oct 2020 03:06:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D75E421D81 for ; Wed, 14 Oct 2020 03:06:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729244AbgJNDGn (ORCPT ); Tue, 13 Oct 2020 23:06:43 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:43587 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729105AbgJNDGn (ORCPT ); Tue, 13 Oct 2020 23:06:43 -0400 Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 09E36UlX012534; Wed, 14 Oct 2020 05:06:30 +0200 Date: Wed, 14 Oct 2020 05:06:30 +0200 From: Willy Tarreau To: Jakub Kicinski Cc: Nicolas Ferre , Claudiu Beznea , netdev@vger.kernel.org, David Miller Subject: Re: [PATCH net-next 0/3] macb: support the 2-deep Tx queue on at91 Message-ID: <20201014030630.GA12531@1wt.eu> References: <20201011090944.10607-1-w@1wt.eu> <20201013170358.1a4d282a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201013170358.1a4d282a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> User-Agent: Mutt/1.6.1 (2016-04-27) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Oct 13, 2020 at 05:03:58PM -0700, Jakub Kicinski wrote: > On Sun, 11 Oct 2020 11:09:41 +0200 Willy Tarreau wrote: > > while running some tests on my Breadbee board, I noticed poor network > > Tx performance. I had a look at the driver (macb, at91ether variant) > > and noticed that at91ether_start_xmit() immediately stops the queue > > after sending a frame and waits for the interrupt to restart the queue, > > causing a dead time after each packet is sent. > > > > The AT91RM9200 datasheet states that the controller supports two frames, > > one being sent and the other one being queued, so I performed minimal > > changes to support this. The transmit performance on my board has > > increased by 50% on medium-sized packets (HTTP traffic), and with large > > packets I can now reach line rate. > > > > Since this driver is shared by various platforms, I tried my best to > > isolate and limit the changes as much as possible and I think it's pretty > > reasonable as-is. I've run extensive tests and couldn't meet any > > unexpected situation (no stall, overflow nor lockup). > > > > There are 3 patches in this series. The first one adds the missing > > interrupt flag for RM9200 (TBRE, indicating the tx buffer is willing > > to take a new packet). The second one replaces the single skb with a > > 2-array and uses only index 0. It does no other change, this is just > > to prepare the code for the third one. The third one implements the > > queue. Packets are added at the tail of the queue, the queue is > > stopped at 2 packets and the interrupt releases 0, 1 or 2 depending > > on what the transmit status register reports. > > LGTM. There's always a chance that this will make other > designs explode, but short of someone from Cadence giving > us a timely review we have only one way to find that out.. :) Not that much in fact, given that the at91ether_* functions are only used by AT91RM9200 (whose datasheet I used to do this) and Mstar which I used for the tests. I initially wanted to get my old SAM9G20 board to boot until I noticed that it doesn't even use the same set of functions, so the potential victims are extremely limited :-) > Applied, thanks! Thank you! Willy