Re: [PATCH v2 net-next 21/26] ice: add XDP and XSK generic per-channel statistics

[Daniel Borkmann <daniel@iogearbox.net>]

On 11/26/21 11:27 PM, Daniel Borkmann wrote:
> On 11/26/21 7:06 PM, Jakub Kicinski wrote:
[...]
>> The information required by the admin is higher level. As you say the
>> primary concern there is "how many packets did XDP eat".
> 
> Agree. Above said, for XDP_DROP I would see one use case where you compare
> different drivers or bond vs no bond as we did in the past in [0] when
> testing against a packet generator (although I don't see bond driver covered
> in this series here yet where it aggregates the XDP stats from all bond slave
> devs).
> 
> On a higher-level wrt "how many packets did XDP eat", it would make sense
> to have the stats for successful XDP_{TX,REDIRECT} given these are out
> of reach from a BPF prog PoV - we can only count there how many times we
> returned with XDP_TX but not whether the pkt /successfully made it/.
> 
> In terms of error cases, could we just standardize all drivers on the behavior
> of e.g. mlx5e_xdp_handle(), meaning, a failure from XDP_{TX,REDIRECT} will
> hit the trace_xdp_exception() and then fallthrough to bump a drop counter
> (same as we bump in XDP_DROP then). So the drop counter will account for
> program drops but also driver-related drops.
> 
> At some later point the trace_xdp_exception() could be extended with an error
> code that the driver would propagate (given some of them look quite similar
> across drivers, fwiw), and then whoever wants to do further processing with
> them can do so via bpftrace or other tooling.

Just thinking out loud, one straight forward example we could start out with
that is also related to Paolo's series [1] ...

enum xdp_error {
	XDP_UNKNOWN,
	XDP_ACTION_INVALID,
	XDP_ACTION_UNSUPPORTED,
};

... and then bpf_warn_invalid_xdp_action() returns one of the latter two
which we pass to trace_xdp_exception(). Later there could be XDP_DRIVER_*
cases e.g. propagated from XDP_TX error exceptions.

         [...]
         default:
                 err = bpf_warn_invalid_xdp_action(act);
                 fallthrough;
         case XDP_ABORTED:
xdp_abort:
                 trace_xdp_exception(rq->netdev, prog, act, err);
                 fallthrough;
         case XDP_DROP:
                 lrstats->xdp_drop++;
                 break;
         }
         [...]

   [1] https://lore.kernel.org/netdev/cover.1637924200.git.pabeni@redhat.com/

> So overall wrt this series: from the lrstats we'd be /dropping/ the pass,
> tx_errors, redirect_errors, invalid, aborted counters. And we'd be /keeping/
> bytes & packets counters that XDP sees, (driver-)successful tx & redirect
> counters as well as drop counter. Also, XDP bytes & packets counters should
> not be counted twice wrt ethtool stats.
> 
>    [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9e2ee5c7e7c35d195e2aa0692a7241d47a433d1e