netdev - Re: consistency for statistics with XDP mode

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Date:   Fri, 30 Nov 2018 20:10:58 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "toke@...e.dk" <toke@...e.dk>,
        "dsahern@...il.com" <dsahern@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "pstaszewski@...are.pl" <pstaszewski@...are.pl>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "mst@...hat.com" <mst@...hat.com>
Subject: Re: consistency for statistics with XDP mode

On Thu, 2018-11-22 at 18:00 +0100, Toke Høiland-Jørgensen wrote:
> David Ahern <dsahern@...il.com> writes:
> 
> > On 11/22/18 1:26 AM, Toke Høiland-Jørgensen wrote:
> > > Saeed Mahameed <saeedm@...lanox.com> writes:
> > > 
> > > > > > I'd say it sounds reasonable to include XDP in the normal
> > > > > > traffic
> > > > > > counters, but having the detailed XDP-specific counters is
> > > > > > quite
> > > > > > useful
> > > > > > as well... So can't we do both (for all drivers)?
> > > > > > 
> > > > 
> > > > What are you thinking ? 
> > > > reporting XDP_DROP in interface dropped counter ?
> > > > and XDP_TX/REDIRECT in the TX counter ?
> > > > XDP_ABORTED in the  err/drop counter ?
> > > > 
> > > > how about having a special XDP command in the .ndo_bpf that
> > > > would query
> > > > the standardized XDP stats ?
> > > the XDP-specific stats are useful to have separately as well :)
> > > 
> > 
> > I would like to see basic packets, bytes, and dropped counters
> > tracked
> > for Rx and Tx via the standard netdev counters for all devices. 

The problem of reporting XDP_DROP in the netedev drop counter is that
they don't fit this counter description : "no space in linux buffers"
and it will be hard for the user to determine whether these drops are
coming from XDP or because no buffer is available, which will make it
impossible to estimate packet rate performance without looking at
ethtool stats.
And reporting XDP_DROP in the netdev rx packets counter is somehow
misleading.. since those packets never made it out of this driver.. 


And reporting XDP_DROP in the netdev rx packets counter is somehow
misleading.. since those packets never made it out of this driver..
> > for ease in accounting as well as speed and simplicity for bumping
> > counters for virtual devices from bpf helpers.
> > 
> > From there, the XDP ones can be in the driver private stats as they
> > are
> > currently but with some consistency across drivers for redirects,
> > drops,
> > any thing else.
> > 
> > So not a radical departure from where we are today, just getting
> > the
> > agreement for consistency and driver owners to make the changes.
> 
> Sounds good to me :)
> 
> -Toke