From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760017AbcLAToB (ORCPT ); Thu, 1 Dec 2016 14:44:01 -0500 Received: from shards.monkeyblade.net ([184.105.139.130]:42660 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752257AbcLATn7 (ORCPT ); Thu, 1 Dec 2016 14:43:59 -0500 Date: Thu, 01 Dec 2016 14:43:57 -0500 (EST) Message-Id: <20161201.144357.33718747165573960.davem@davemloft.net> To: andreyknvl@google.com Cc: herbert@gondor.apana.org.au, jasowang@redhat.com, edumazet@google.com, pmk@google.com, pabeni@redhat.com, mst@redhat.com, soheil@google.com, elfring@users.sourceforge.net, rppt@linux.vnet.ibm.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, dvyukov@google.com, kcc@google.com, syzkaller@googlegroups.com Subject: Re: [PATCH v2] tun: Use netif_receive_skb instead of netif_rx From: David Miller In-Reply-To: <1480584880-48651-1-git-send-email-andreyknvl@google.com> References: <1480584880-48651-1-git-send-email-andreyknvl@google.com> X-Mailer: Mew version 6.7 on Emacs 24.5 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Thu, 01 Dec 2016 10:44:35 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrey Konovalov Date: Thu, 1 Dec 2016 10:34:40 +0100 > This patch changes tun.c to call netif_receive_skb instead of netif_rx > when a packet is received (if CONFIG_4KSTACKS is not enabled to avoid > stack exhaustion). The difference between the two is that netif_rx queues > the packet into the backlog, and netif_receive_skb proccesses the packet > in the current context. > > This patch is required for syzkaller [1] to collect coverage from packet > receive paths, when a packet being received through tun (syzkaller collects > coverage per process in the process context). > > As mentioned by Eric this change also speeds up tun/tap. As measured by > Peter it speeds up his closed-loop single-stream tap/OVS benchmark by > about 23%, from 700k packets/second to 867k packets/second. > > A similar patch was introduced back in 2010 [2, 3], but the author found > out that the patch doesn't help with the task he had in mind (for cgroups > to shape network traffic based on the original process) and decided not to > go further with it. The main concern back then was about possible stack > exhaustion with 4K stacks. > > [1] https://github.com/google/syzkaller > > [2] https://www.spinics.net/lists/netdev/thrd440.html#130570 > > [3] https://www.spinics.net/lists/netdev/msg130570.html > > Signed-off-by: Andrey Konovalov > --- > > Changes since v1: > - incorporate Eric's note about speed improvements in commit description > - use netif_receive_skb CONFIG_4KSTACKS is not enabled Applied to net-next, thanks!