From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754339Ab0IOPKY (ORCPT ); Wed, 15 Sep 2010 11:10:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51309 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754293Ab0IOPKU (ORCPT ); Wed, 15 Sep 2010 11:10:20 -0400 Date: Wed, 15 Sep 2010 17:04:12 +0200 From: "Michael S. Tsirkin" To: Shirley Ma Cc: Arnd Bergmann , Avi Kivity , "Xin, Xiaohui" , David Miller , netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel Message-ID: <20100915150412.GA679@redhat.com> References: <20100914162952.GB13560@redhat.com> <1284483745.13351.71.camel@localhost.localdomain> <20100914182707.GB15549@redhat.com> <1284490143.13351.82.camel@localhost.localdomain> <20100914190156.GA16037@redhat.com> <1284492983.13351.95.camel@localhost.localdomain> <20100915051241.GA25340@redhat.com> <1284531675.24603.259.camel@localhost.localdomain> <20100915101000.GB28016@redhat.com> <1284562354.2573.12.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1284562354.2573.12.camel@localhost.localdomain> User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 15, 2010 at 07:52:34AM -0700, Shirley Ma wrote: > On Wed, 2010-09-15 at 12:10 +0200, Michael S. Tsirkin wrote: > > Another issue is that macvtap can be bound to almost > > anything, including e.g. a tap device or a bridge, > > which might hang on to skb fragments for unlimited time. > > Zero copy TX won't easily work there. > > I can imagine either somehow triggering a data copy after the > > fact (hard), or detecting such devices and avoiding > > zero copy (unfortunate for guest to guest, and drivers > > will need tuning). > > So far macvtap zero copy patch is limited to lower devices supports high > memory DMA, it doesn't apply to a tap device or a bridge. Okay. What about macvtap in bridge mode? > > > Don't you think once I address vhost_add_used_and_signal update > > > issue, it is a simple and complete patch for macvtap TX zero copy? > > > > > > Thanks > > > Shirley > > > > I like the fact that the patch is simple. Unfortunately > > I suspect it'll stop being simple by the time it's complete :) > > I can make a try. :) > > Thanks > Shirley