From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756687Ab2FYMwx (ORCPT ); Mon, 25 Jun 2012 08:52:53 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:34487 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756388Ab2FYMwv (ORCPT ); Mon, 25 Jun 2012 08:52:51 -0400 Subject: Re: [PATCH 5/6] tuntap: per queue 64 bit stats From: Eric Dumazet To: Jason Wang 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 In-Reply-To: <1340625563-9300-6-git-send-email-jasowang@redhat.com> References: <20120625060830.6765.27584.stgit@amd-6168-8-1.englab.nay.redhat.com> <1340625563-9300-6-git-send-email-jasowang@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 25 Jun 2012 14:52:45 +0200 Message-ID: <1340628765.10893.46.camel@edumazet-glaptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. I suggest this patch comes before 'tuntap: multiqueue support' in the serie.