From owner-freebsd-net@FreeBSD.ORG Tue Sep 18 12:34:51 2012 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 9639E10657DC; Tue, 18 Sep 2012 12:34:51 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (bigknife-pt.tunnel.tserv9.chi1.ipv6.he.net [IPv6:2001:470:1f10:75::2]) by mx1.freebsd.org (Postfix) with ESMTP id 69ACF8FC15; Tue, 18 Sep 2012 12:34:51 +0000 (UTC) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id B7D93B911; Tue, 18 Sep 2012 08:34:50 -0400 (EDT) From: John Baldwin To: freebsd-net@freebsd.org Date: Tue, 18 Sep 2012 07:58:42 -0400 User-Agent: KMail/1.13.5 (FreeBSD/8.2-CBSD-20110714-p17; KDE/4.5.5; amd64; ; ) References: <201209171622.11157.jhb@freebsd.org> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201209180758.42299.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Tue, 18 Sep 2012 08:34:50 -0400 (EDT) Cc: Adrian Chadd , Ryan Stone , Jack Vogel Subject: Re: What's the latest on fixing IFF_DRV_OACTIVE/if_start/etc? X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 18 Sep 2012 12:34:51 -0000 On Monday, September 17, 2012 4:29:50 pm Jack Vogel wrote: > On Mon, Sep 17, 2012 at 1:22 PM, John Baldwin wrote: > > > On Monday, September 17, 2012 4:00:04 pm Jack Vogel wrote: > > > So, you mean having them create their own buf ring I assume? Would be > > easy > > > enough to hack some code and try it if someone is so inclined? > > > > No, that would be backwards (back to giving them a queue). Adrian's > > suggestion is to provide a mechanism so that the "real" interface > > (e.g. emX) can call back into the psuedo-interfaces on top of it > > (vlanX or bridgeX) when a TX completion interrupt fires so that the > > pseudo-interface would know to restart transmission. However, I think > > this is generally not ideal. I don't think we want an additional queue > > of pending packets in things like if_bridge(4) and vlan(4). If the > > underlying physical interface(s) are full, the packet should just get > > dropped rather than queued. Using if_transmit directly will do that while > > avoiding overhead. Also, making the callback work would also be a bit > > ungainly. > > > > > I meant using if_transmit, not the callback, would it not then need a buf > ring? No. You only need a buf_ring if you want a software queue of packets. In the case of virtual interfaces you don't really want that (it leads to double queueing). Instead, you want things like vlan(4) to just be a simple transform that slaps on a vlan header and then passes the packet to the underlying interface. You wouldn't want to have a software queue at various protocol layers that slap on headers (e.g. Ethernet or IP), and things like vlan(4) shouldn't have one either. -- John Baldwin