Re: [PATCH 5/6] tuntap: per queue 64 bit stats

On 06/25/2012 08:52 PM, Eric Dumazet wrote:

On Mon, 2012-06-25 at 19:59 +0800, Jason Wang wrote:

quoted

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.