netdev - Re: [PATCH bpf-next v2 1/2] xdp: Move devmap bulk queue into struct net

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Date:   Thu, 16 Jan 2020 14:51:41 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...il.com>,
        John Fastabend <john.fastabend@...il.com>, brouer@...hat.com
Subject: Re: [PATCH bpf-next v2 1/2] xdp: Move devmap bulk queue into struct net_device

Jesper Dangaard Brouer <brouer@...hat.com> writes:

> On Wed, 15 Jan 2020 23:11:21 +0100
> Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
>> Jesper Dangaard Brouer <brouer@...hat.com> writes:
>> 
>> > On Mon, 13 Jan 2020 19:10:55 +0100
>> > Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>> >  
>> >> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
>> >> index da9c832fc5c8..030d125c3839 100644
>> >> --- a/kernel/bpf/devmap.c
>> >> +++ b/kernel/bpf/devmap.c  
>> > [...]  
>> >> @@ -346,8 +340,7 @@ static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags)
>> >>  out:
>> >>  	bq->count = 0;
>> >>  
>> >> -	trace_xdp_devmap_xmit(&obj->dtab->map, obj->idx,
>> >> -			      sent, drops, bq->dev_rx, dev, err);
>> >> +	trace_xdp_devmap_xmit(NULL, 0, sent, drops, bq->dev_rx, dev, err);  
>> >
>> > Hmm ... I don't like that we lose the map_id and map_index identifier.
>> > This is part of our troubleshooting interface.  
>> 
>> Hmm, I guess I can take another look at whether there's a way to avoid
>> that. Any ideas?
>
> Looking at the code and the other tracepoints...
>
> I will actually suggest to remove these two arguments, because the
> trace_xdp_redirect_map tracepoint also contains the ifindex'es, and to
> troubleshoot people can record both tracepoints and do the correlation
> themselves.
>
> When changing the tracepoint I would like to keep member 'drops' and
> 'sent' at the same struct offsets.  As our xdp_monitor example reads
> these and I hope we can kept it working this way.
>
> I've coded it up, and tested it.  The new xdp_monitor will work on
> older kernels, but the old xdp_monitor will fail attaching on newer
> kernels. I think this is fair enough, as we are backwards compatible.

SGTM - thanks! I'll respin and include this :)

-Toke