netdev - Re: [PATCH v3 bpf-next] cpumap: bulk skb using netif_receive_skb

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Date:   Thu, 22 Apr 2021 12:59:31 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>,
        BPF-dev-list <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <song@...nel.org>,
        Toke Hoiland Jorgensen <toke@...hat.com>
Subject: Re: [PATCH v3 bpf-next] cpumap: bulk skb using netif_receive_skb_list

>
> [...]
> > > +   TP_ARGS(map_id, processed, sched, xdp_stats),
> > >
> > >     TP_STRUCT__entry(
> > >             __field(int, map_id)
> > >             __field(u32, act)
> > >             __field(int, cpu)
> > > -           __field(unsigned int, drops)
> > >             __field(unsigned int, processed)
> >
> > So, struct member @processed will takeover the room for @drops.
> >
> > Can you please test how an old xdp_monitor program will react to this?
> > Will it fail, or extract and show wrong values?
>
> Ack, right. I think we should keep the struct layout in order to maintain
> back-compatibility. I will fix it in v4.
>
> >
> > The xdp_mointor tool is in several external git repos:
> >
> >  https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/samples/bpf/xdp_monitor_kern.c
> >  https://github.com/xdp-project/xdp-tutorial/tree/master/tracing02-xdp-monitor

Running an old version of xdp_monitor with a patched kernel, I
verified the xdp sample does not crash but it reports wrong values
(e.g. pps are reported as drops for tracepoint disagliment).
I think we have two possibilities here:
- assuming tracepoints are not a stable ABI, we can just fix xdp
samples available in the kernel tree and provide a patch for
xdp-project
- keep current tracepoint layout and just rename current drop variable
in bpf/cpumap.c in something like skb_alloc_drop.

I am not against both of them. What do you think?

Regards,
Lorenzo

> >
> > Do you have any plans for fixing those tools?
>
> I update xdp_monitor_{kern,user}.c and xdp_redirect_cpu_{kern,user}.c in the
> patch. Do you mean to post a dedicated patch for xdp-project tutorial?
>
> Regards,
> Lorenzo
>
> >
> >
> >
> >
> > --
> > Best regards,
> >   Jesper Dangaard Brouer
> >   MSc.CS, Principal Kernel Engineer at Red Hat
> >   LinkedIn: http://www.linkedin.com/in/brouer
> >