Re: [RFC PATCH 4/5] mlx4: add support for fast rx drop bpf program

[Eran Ben Elisha <eranlinuxmellanox@gmail.com>]

On Tue, Apr 5, 2016 at 5:20 AM, Brenden Blanco <bblanco@plumgrid.com> wrote:
> On Sat, Apr 02, 2016 at 11:15:38PM -0700, Brenden Blanco wrote:
>> On Fri, Apr 01, 2016 at 07:08:31PM -0700, Eric Dumazet wrote:
> [...]
>> > 2) priv->stats.rx_dropped is shared by all the RX queues -> false
>> > sharing.
>> >
>> >    This is probably the right time to add a rx_dropped field in struct
>> > mlx4_en_rx_ring since you guys want to drop 14 Mpps, and 50 Mpps on
>> > higher speed links.
>> >
>> This sounds reasonable! Will look into it for the next spin.
> I looked into this, and it seems to me that both the rx and tx dropped
> stats are buggy. With commit a3333b35da1634f49aca541f2574a084221e2616,
> specifically with the line
>   stats->rx_dropped = be32_to_cpu(mlx4_en_stats->RDROP);
> that occurs during the periodic ethtool task, whatever ++ was happening
> in the rx/tx code is overwritten with the HW value. Since the SW stats
> are incremented mostly in edge (oom) cases, nobody probably noticed. To
> me it doesn't seem right to mix hard and soft counters, especially at
> the risk of making a bad situation worse, so I'm planning to omit the
> new bpf dropped++ stat and we can discuss ways to fix this other bug
> separately.

Thanks Eric and Brenden,
I will make a patch for mlx4_en RX dropped counters to fix the issues
you raised here.