From owner-svn-src-all@FreeBSD.ORG Wed Jun 5 06:14:49 2013 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 6F55923D for ; Wed, 5 Jun 2013 06:14:49 +0000 (UTC) (envelope-from bounces+73574-8822-svn-src-all=freebsd.org@sendgrid.me) Received: from o3.shared.sendgrid.net (o3.shared.sendgrid.net [208.117.48.85]) by mx1.freebsd.org (Postfix) with SMTP id F13621688 for ; Wed, 5 Jun 2013 06:14:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sendgrid.info; h=from :mime-version:to:cc:subject:references:in-reply-to:content-type :content-transfer-encoding; s=smtpapi; bh=iJem3h9WHvJUWDO9RZ5RMd idMSk=; b=McXSDBMo/pYpfQdSvkcrzljqV8WsWztRZeoSoGMdA2pTfzCjJvZHZH wz1awgskmMDYbKCwnsS0YjS+iq6P5AVX8QYuCibEWUlxhuSSjG5h7JcH/d42aPGI uwEjMhhCU9WzFNnEK0iiQUIcRwL68MFnXli/OR00sKKg20NpBFnW4= Received: by 10.42.83.34 with SMTP id filter-123.24595.51AED7582 Wed, 05 Jun 2013 06:14:48 +0000 (UTC) Received: from mail.tarsnap.com (unknown [10.60.208.17]) by mi19 (SG) with ESMTP id 13f12f92f78.482f.16789fd for ; Wed, 05 Jun 2013 01:14:47 -0500 (CST) Received: (qmail 48915 invoked from network); 5 Jun 2013 06:14:46 -0000 Received: from unknown (HELO clamshell.daemonology.net) (127.0.0.1) by ec2-107-20-205-189.compute-1.amazonaws.com with ESMTP; 5 Jun 2013 06:14:46 -0000 Received: (qmail 69478 invoked from network); 5 Jun 2013 06:13:54 -0000 Received: from unknown (HELO clamshell.daemonology.net) (127.0.0.1) by clamshell.daemonology.net with SMTP; 5 Jun 2013 06:13:54 -0000 Message-ID: <51AED722.8000504@freebsd.org> Date: Tue, 04 Jun 2013 23:13:54 -0700 From: Colin Percival User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:17.0) Gecko/20130524 Thunderbird/17.0.6 MIME-Version: 1.0 To: Lawrence Stewart Subject: Re: svn commit: r251297 - head/sys/dev/xen/netfront References: <201306031300.r53D0XUx092178@svn.freebsd.org> <51AED1F3.2060003@freebsd.org> In-Reply-To: <51AED1F3.2060003@freebsd.org> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SG-EID: A6W2xSVPHetogaU8rnzccWwgBYtN+QvIzXyjfe/10PFt7odERcTzFE6iBL5iSTO14jKdo/jsgr8RmgoUPN0ZU9fIel8UAjsQXcCi5P4h0WY6jGeIg5YNI414l+qUEkL47qyFUhfYKM/seQ94xzKw8g== Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, Andre Oppermann X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 05 Jun 2013 06:14:49 -0000 On 06/04/13 22:51, Lawrence Stewart wrote: > On 06/03/13 23:00, Andre Oppermann wrote: >> Modified: head/sys/dev/xen/netfront/netfront.c >> ============================================================================== >> --- head/sys/dev/xen/netfront/netfront.c Mon Jun 3 12:55:13 2013 (r251296) >> +++ head/sys/dev/xen/netfront/netfront.c Mon Jun 3 13:00:33 2013 (r251297) >> @@ -134,6 +134,7 @@ static const int MODPARM_rx_flip = 0; >> * to mirror the Linux MAX_SKB_FRAGS constant. >> */ >> #define MAX_TX_REQ_FRAGS (65536 / PAGE_SIZE + 2) >> +#define NF_TSO_MAXBURST ((IP_MAXPACKET / PAGE_SIZE) * MCLBYTES) > > For posterity's sake, can you and/or Colin please elaborate on how this > value was determined and what it is dependent upon? Could a newer > version of Xen remove the need for this reduced limit? The comment above (of which only the last line is quoted in the diff) explains it: * This limit is imposed by the backend driver. We assume here that * we are dealing with a Linux driver domain and have set our limit * to mirror the Linux MAX_SKB_FRAGS constant. This isn't a Xen issue really; rather, it's a Linux Dom0 issue. AFAIK there are no changes in the pipe to fix this in Linux; but this would not be needed with a different Dom0 (e.g., a FreeBSD Dom0, if/when that becomes possible) or if FreeBSD switched to using 4kB mbuf clusters (since at that point we would be matching Linux and be able to fit a maximum-length IP packet into the allowed number of fragments). -- Colin Percival Security Officer Emeritus, FreeBSD | The power to serve Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid