From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752082AbZHMGHh (ORCPT ); Thu, 13 Aug 2009 02:07:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751204AbZHMGHh (ORCPT ); Thu, 13 Aug 2009 02:07:37 -0400 Received: from mx2.redhat.com ([66.187.237.31]:43357 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751153AbZHMGHg (ORCPT ); Thu, 13 Aug 2009 02:07:36 -0400 Date: Thu, 13 Aug 2009 09:06:15 +0300 From: "Michael S. Tsirkin" To: Arnd Bergmann Cc: virtualization@lists.linux-foundation.org, "Ira W. Snyder" , netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] vhost_net: a kernel-level virtio server Message-ID: <20090813060615.GC3029@redhat.com> References: <200908121903.22325.arnd@arndb.de> <20090812172141.GA29966@redhat.com> <200908121959.47222.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200908121959.47222.arnd@arndb.de> 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 On Wed, Aug 12, 2009 at 07:59:47PM +0200, Arnd Bergmann wrote: > The trick is to swap the virtqueues instead. virtio-net is actually > mostly symmetric in just the same way that the physical wires on a > twisted pair ethernet are symmetric (I like how that analogy fits). You need to really squint hard for it to look symmetric. For example, for RX, virtio allocates an skb, puts a descriptor on a ring and waits for host to fill it in. Host system can not do the same: guest does not have access to host memory. You can do a copy in transport to hide this fact, but it will kill performance. -- MST