From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 5/6] tuntap: per queue 64 bit stats\ Date: Tue, 26 Jun 2012 22:46:34 +0300 Message-ID: <20120626194634.GA14054@redhat.com> 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> <4FE95015.7000707@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Dumazet , 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 To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <4FE95015.7000707@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Jun 26, 2012 at 02:00:53PM +0800, Jason Wang wrote: > 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(). Or make them per cpu as most everyone did. > >I suggest this patch comes before 'tuntap: multiqueue support' in the > >serie. > > Sure, thanks. > > > > > >