From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jason Wang <jasowang@redhat.com>
Subject: Re: [PATCH 5/6] tuntap: per queue 64 bit stats
Date: Tue, 26 Jun 2012 14:00:53 +0800
Message-ID: <4FE95015.7000707@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>
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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
To: Eric Dumazet <eric.dumazet@gmail.com>
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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.
>
>
>