Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756727Ab1ERJGY (ORCPT ); Wed, 18 May 2011 05:06:24 -0400 Received: from mail-qy0-f174.google.com ([209.85.216.174]:61362 "EHLO mail-qy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755816Ab1ERJGW convert rfc822-to-8bit (ORCPT ); Wed, 18 May 2011 05:06:22 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=mHCizrZkjitGY6IF8Hpw31HwBotgLTWQ5b3p427P2ZaSjvQx7jm2xiV1WTtDg2MHlv nd7596J2zMVhzxK/qrFrczGzNfXBtH0rf86fvQJx9fcoBNNeZLpBoJsZjJC6PPSloXJw l0bbHQMBhHfY+xrASIOAqaspSItLzPNeDbPt8= MIME-Version: 1.0 In-Reply-To: <1305675865.10756.63.camel@localhost.localdomain> References: <1305574128.3456.23.camel@localhost.localdomain> <1305574518.2885.25.camel@bwh-desktop> <1305574680.3456.33.camel@localhost.localdomain> <1305575253.2885.28.camel@bwh-desktop> <20110516211459.GE18148@redhat.com> <1305588738.3456.65.camel@localhost.localdomain> <1305671318.10756.49.camel@localhost.localdomain> <1305675865.10756.63.camel@localhost.localdomain> From: =?ISO-8859-2?Q?Micha=B3_Miros=B3aw?= Date: Wed, 18 May 2011 11:06:00 +0200 Message-ID: Subject: Re: [PATCH V5 2/6 net-next] netdevice.h: Add zero-copy flag in netdevice To: Shirley Ma Cc: "Michael S. Tsirkin" , Ben Hutchings , David Miller , Eric Dumazet , Avi Kivity , Arnd Bergmann , netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2081 Lines: 48 W dniu 18 maja 2011 01:44 u?ytkownik Shirley Ma napisa?: > On Wed, 2011-05-18 at 00:58 +0200, Micha? Miros?aw wrote: >> W dniu 18 maja 2011 00:28 u?ytkownik Shirley Ma >> napisa?: >> > On Tue, 2011-05-17 at 23:48 +0200, Micha? Miros?aw wrote: >> >> 2011/5/17 Shirley Ma : >> >> > Looks like to use a new flag requires more time/work. I am >> thinking >> >> > whether we can just use HIGHDMA flag to enable zero-copy in >> macvtap >> >> to >> >> > avoid the new flag for now since mavctap uses real NICs as lower >> >> device? >> >> >> >> Is there any other restriction besides requiring driver to not >> recycle >> >> the skb? Are there any drivers that recycle TX skbs? >> > Not more other restrictions, skb clone is OK. pskb_expand_head() >> looks >> > OK to me from code review. >> >> > Currently there is no drivers recycle TX skbs. >> >> So why do you require the target device to have some flags at all? > We could use macvtap to check lower device HIGHDMA to enable zero-copy, > but I am not sure whether it is sufficient. If it's sufficient then we > don't need to use a new flag here. To be safe, it's better to use a new > flag to enable each device who can pass zero-copy test. >> Do I understand correctly, that this zero-copy feature is about >> packets received from VMs? > Yes, packets sent from VMs, and received in local host for TX zero-copy > here. What is the zero-copy test? On some arches the HIGHDMA is not needed at all so might be not enabled on anything. It looks like the correct test would be per-packet check of !illegal_highdma() or maybe NETIF_F_SG as returned from harmonize_features(). For virtual devices or other software forwarding this might lead to skb_linearize() in some cases, but is it that bad? Best Regards, Micha? Miros?aw -- 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/