From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752538Ab2GVTkX (ORCPT ); Sun, 22 Jul 2012 15:40:23 -0400 Received: from shards.monkeyblade.net ([149.20.54.216]:38153 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752430Ab2GVTkV (ORCPT ); Sun, 22 Jul 2012 15:40:21 -0400 Date: Sun, 22 Jul 2012 12:40:20 -0700 (PDT) Message-Id: <20120722.124020.1299343386554149788.davem@davemloft.net> To: mst@redhat.com Cc: jasowang@redhat.com, eric.dumazet@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ebiederm@xmission.com, Ian.Campbell@citrix.com Subject: Re: [PATCHv3 0/6] tun zerocopy support From: David Miller In-Reply-To: <20120721220534.GA22912@redhat.com> References: <20120720.174902.2055189237500355771.davem@davemloft.net> <20120721220534.GA22912@redhat.com> X-Mailer: Mew version 6.5 on Emacs 24.0.97 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Michael S. Tsirkin" Date: Sun, 22 Jul 2012 01:05:34 +0300 > I agree a small win in CPU use is nothing to write home about, > I don't yet understand why the win is so small - macvtap has zero copy > supported for a while and it has exactly same issues. > I hope adding tun zerocopy support upstream will help us > make progress faster and find the bottleneck, so far not many people use > macvtap so zero copy mode there didn't make progress. > > I do know why local performance regresses with zero copy enabled: > instead of plain copy to user we got get user pages and then memcpy. > We'll need some logic here to detect this and turn off zero copy. > > The core patches will also be helpful for Ian's more ambitious work. > > Overall I think it's a step in the right direction and it's easier to > work if core parts are upstream, but if you think we need to wait > until the gains are more significant, I understand that too. Ok, I've applied this series, let's see what happens.