From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757761Ab2FZF7H (ORCPT ); Tue, 26 Jun 2012 01:59:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60882 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752501Ab2FZF7F (ORCPT ); Tue, 26 Jun 2012 01:59:05 -0400 Message-ID: <4FE95015.7000707@redhat.com> Date: Tue, 26 Jun 2012 14:00:53 +0800 From: Jason Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120210 Thunderbird/10.0.1 MIME-Version: 1.0 To: Eric Dumazet CC: mst@redhat.com, akong@redhat.com, habanero@linux.vnet.ibm.com, tahm@linux.vnet.ibm.com, haixiao@juniper.net, jwhan@filewood.snu.ac.kr, ernesto.martin@viasat.com, mashirle@us.ibm.com, davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, krkumar2@in.ibm.com, shemminger@vyatta.com, edumazet@google.com Subject: Re: [PATCH 5/6] tuntap: per queue 64 bit stats References: <20120625060830.6765.27584.stgit@amd-6168-8-1.englab.nay.redhat.com> <1340625563-9300-6-git-send-email-jasowang@redhat.com> <1340628765.10893.46.camel@edumazet-glaptop> In-Reply-To: <1340628765.10893.46.camel@edumazet-glaptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/25/2012 08:52 PM, Eric Dumazet wrote: > On Mon, 2012-06-25 at 19:59 +0800, Jason Wang wrote: >> As we've added multiqueue support for tun/tap, this patch convert the statistics >> to use per-queue 64 bit statistics. > LLTX means you can have several cpus calling TX path in parallel. > > So tx stats are wrong (even before this patch), and racy after this > patch (if several cpu access same queue, it seems to be possible) > > u64_stats_update_begin(&tfile->stats.tx_syncp); > tfile->stats.tx_packets++; > tfile->stats.tx_bytes += total; > u64_stats_update_end(&tfile->stats.tx_syncp); > > This can break horribly if several cpus run this code using same 'tfile' > pointer. Yes, looks like it's hard to use NETIF_F_LLTX without breaking the u64 statistics, may worth to use tx lock and alloc_netdev_mq(). > I suggest this patch comes before 'tuntap: multiqueue support' in the > serie. Sure, thanks. > > >