From owner-freebsd-net@FreeBSD.ORG Mon Sep 8 05:53:32 2014 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id EA1DC6F9; Mon, 8 Sep 2014 05:53:32 +0000 (UTC) Received: from mail.turbocat.net (heidi.turbocat.net [88.198.202.214]) (using TLSv1.1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id A4C071904; Mon, 8 Sep 2014 05:53:31 +0000 (UTC) Received: from laptop015.home.selasky.org (cm-176.74.213.204.customer.telag.net [176.74.213.204]) (using TLSv1 with cipher ECDHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by mail.turbocat.net (Postfix) with ESMTPSA id 32B0E1FE027; Mon, 8 Sep 2014 07:53:23 +0200 (CEST) Message-ID: <540D444C.6090904@selasky.org> Date: Mon, 08 Sep 2014 07:53:16 +0200 From: Hans Petter Selasky User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Rick Macklem Subject: Re: [RFC] Patch to improve TSO limitation formula in general References: <1762951742.33012989.1409954952800.JavaMail.root@uoguelph.ca> In-Reply-To: <1762951742.33012989.1409954952800.JavaMail.root@uoguelph.ca> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-net@freebsd.org, Eric Joyner , FreeBSD Current , Scott Long , Jack F Vogel X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 08 Sep 2014 05:53:33 -0000 On 09/06/14 00:09, Rick Macklem wrote: > Hans Petter Selesky wrote: >> On 09/05/14 23:19, Eric Joyner wrote: >>> There are some concerns if we use this with devices that ixl >>> supports: >>> >>> - The maximum fragment size is 16KB-1, which isn't a power of 2. >>> >> >> Hi Eric, >> >> Multiplying by powers of two are more fast, than non-powers of two. >> So >> in this case you would have to use 8KB as a maximum. >> > Well, I'm no architecture expert, but I really doubt the CPU delay of a > non-power of 2 multiply/divide is significant related to doing smaller > TSO segments. Long ago (as in 1970s) I did work on machines where shifts > for power of 2 multiply/divide was preferable, but these days I doubt it > is going to matter?? > >>> - You can't get the maximum TSO size for ixl devices by multiplying >>> the >>> maximum number of fragments by the maximum size. >>> Instead the number of fragments is AFAIK unlimited, but a segment >>> can only >>> span 8 mbufs (including the [up to 3] mbufs containing the header), >>> and the >>> maximum TSO size is 256KB. Hi, Maybe that can be a separate parameter? I see that your patch assumes that a segment can be any-length. That is not always the case. Remember there are JUMBO mbufs too. With my patch, the maximum segment size is a separate parameter. The total number of TSO bytes is then not so useful. --HPS