Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932381Ab0DGITt (ORCPT ); Wed, 7 Apr 2010 04:19:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40895 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756064Ab0DGITn (ORCPT ); Wed, 7 Apr 2010 04:19:43 -0400 Date: Wed, 7 Apr 2010 11:15:32 +0300 From: "Michael S. Tsirkin" To: "Xin, Xiaohui" Cc: "netdev@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "mingo@elte.hu" , "jdike@c2.user-mode-linux.org" , "yzhao81@gmail.com" Subject: Re: [PATCH 1/3] A device for zero-copy based on KVM virtio-net. Message-ID: <20100407081532.GB9550@redhat.com> References: <20100308112849.GI7482@redhat.com> <1270114038-5048-1-git-send-email-xiaohui.xin@intel.com> <20100401110841.GE3323@redhat.com> <97F6D3BD476C464182C1B7BABF0B0AF5C183234A@shzsmsx502.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <97F6D3BD476C464182C1B7BABF0B0AF5C183234A@shzsmsx502.ccr.corp.intel.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 992 Lines: 27 On Wed, Apr 07, 2010 at 10:41:08AM +0800, Xin, Xiaohui wrote: > Michael, > > >> Qemu needs a userspace write, is that a synchronous one or > >>asynchronous one? > > >It's a synchronous non-blocking write. > Sorry, why the Qemu live migration needs the device have a userspace write? > how does the write operation work? And why a read operation is not cared here? > > Thanks > Xiaohui Roughly, with ethernet bridges, moving a device from one location in the network to another makes forwarding tables incorrect (or incomplete), until outgoing traffic from the device causes these tables to be updated. Since there's no guarantee that guest will generate outgoing traffic, after migration qemu sends out several dummy packets itself. -- MST -- 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/