Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751206AbWJIR4b (ORCPT ); Mon, 9 Oct 2006 13:56:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751611AbWJIR4b (ORCPT ); Mon, 9 Oct 2006 13:56:31 -0400 Received: from smtp.osdl.org ([65.172.181.4]:15077 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1750875AbWJIR4a (ORCPT ); Mon, 9 Oct 2006 13:56:30 -0400 Date: Mon, 9 Oct 2006 09:50:51 -0700 From: Stephen Hemminger To: "Michael S. Tsirkin" Cc: Linux Kernel Mailing List , netdev@vger.kernel.org, openib-general@openib.org, Roland Dreier Subject: Re: Dropping NETIF_F_SG since no checksum feature. Message-ID: <20061009095051.38ed9f22@freekitty> In-Reply-To: <20061009174705.GG26849@mellanox.co.il> References: <20061009174705.GG26849@mellanox.co.il> Organization: OSDL X-Mailer: Sylpheed-Claws 2.5.0-rc3 (GTK+ 2.10.6; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1862 Lines: 43 On Mon, 9 Oct 2006 19:47:05 +0200 "Michael S. Tsirkin" wrote: > Hi! > I'm trying to build a network device driver supporting a very large MTU (around 64K) > on top of an infiniband connection, and I've hit a couple of issues I'd > appreciate some feedback on: > > 1. On the send side, > I've set NETIF_F_SG, but hardware does not support checksum offloading, > and I see "dropping NETIF_F_SG since no checksum feature" warning, > and I seem to be getting large packets all in one chunk. > The reason I've set NETIF_F_SG, is because I'm concerned that under real life > stress Linux won't be able to allocate 64K of continuous memory. > > Is this concern of mine valid? I saw in-tree drivers allocating at least 8K. > What's the best way to enable S/G on send side? > Is checksum offloading really required for S/G? Yes, in the current implementation, Linux needs checksum offload. But there is no reason, your driver can't compute the checksum in software. > 2. On the receive side, what's the best/right way to create an skb that > is larger than PAGE_SIZE? > Do I allocate with alloc_page and fill in nr_frags with skb_fill_page_desc? > Some drivers seem to fill in frag_list - which is better? > I see than even skb_put only works properly on linear skb. Allocating large buffers is problematic on busy systems. See lastest e1000 or sky2 that use frag_list. > What are the helpers legal for fragmented skb? Read the source. Setting up fragmented buffers has less helper functions, but isn't that hard. -- Stephen Hemminger - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/