netdev - Re: [PATCH net-next v6 3/5] bpf: cpumap: implement generic cpumap

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Date:   Fri, 2 Jul 2021 15:33:46 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>, netdev@...r.kernel.org
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Eric Leblond <eric@...it.org>, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v6 3/5] bpf: cpumap: implement generic cpumap


On 02/07/2021 13.18, Kumar Kartikeya Dwivedi wrote:
> This change implements CPUMAP redirect support for generic XDP programs.
> The idea is to reuse the cpu map entry's queue that is used to push
> native xdp frames for redirecting skb to a different CPU. This will
> match native XDP behavior (in that RPS is invoked again for packet
> reinjected into networking stack).
>
> To be able to determine whether the incoming skb is from the driver or
> cpumap, we reuse skb->redirected bit that skips generic XDP processing
> when it is set. To always make use of this, CONFIG_NET_REDIRECT guard on
> it has been lifted and it is always available.
>
>  From the redirect side, we add the skb to ptr_ring with its lowest bit
> set to 1.  This should be safe as skb is not 1-byte aligned. This allows
> kthread to discern between xdp_frames and sk_buff. On consumption of the
> ptr_ring item, the lowest bit is unset.
>
> In the end, the skb is simply added to the list that kthread is anyway
> going to maintain for xdp_frames converted to skb, and then received
> again by using netif_receive_skb_list.
>
> Bulking optimization for generic cpumap is left as an exercise for a
> future patch for now.
>
> Since cpumap entry progs are now supported, also remove check in
> generic_xdp_install for the cpumap.
>
> Reviewed-by: Toke Høiland-Jørgensen<toke@...hat.com>
> Signed-off-by: Kumar Kartikeya Dwivedi<memxor@...il.com>
> ---
>   include/linux/bpf.h    |   9 +++-
>   include/linux/skbuff.h |  10 +---
>   kernel/bpf/cpumap.c    | 116 ++++++++++++++++++++++++++++++++++-------
>   net/core/dev.c         |   3 +-
>   net/core/filter.c      |   6 ++-
>   5 files changed, 114 insertions(+), 30 deletions(-)


Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>