netdev - Re: [PATCH bpf-next v3 2/2] bpf, xdp: restructure redirect actions

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Date:   Mon, 22 Feb 2021 09:10:47 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     brouer@...hat.com, ast@...nel.org, daniel@...earbox.net,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Björn Töpel 
        <bjorn.topel@...el.com>, maciej.fijalkowski@...el.com,
        hawk@...nel.org, toke@...hat.com, magnus.karlsson@...el.com,
        john.fastabend@...il.com, kuba@...nel.org, davem@...emloft.net
Subject: Re: [PATCH bpf-next v3 2/2] bpf, xdp: restructure redirect actions

On Sun, 21 Feb 2021 21:09:54 +0100
Björn Töpel <bjorn.topel@...il.com> wrote:

> From: Björn Töpel <bjorn.topel@...el.com>
> 
> The XDP_REDIRECT implementations for maps and non-maps are fairly
> similar, but obviously need to take different code paths depending on
> if the target is using a map or not. Today, the redirect targets for
> XDP either uses a map, or is based on ifindex.
> 
> Here, an explicit redirect type is added to bpf_redirect_info, instead
> of the actual map. Redirect type, map item/ifindex, and the map_id (if
> any) is passed to xdp_do_redirect().
> 
> In addition to making the code easier to follow, using an explicit
> type in bpf_redirect_info has a slight positive performance impact by
> avoiding a pointer indirection for the map type lookup, and instead
> use the cacheline for bpf_redirect_info.
> 
> Since the actual map is not passed via bpf_redirect_info anymore, the
> map lookup is only done in the BPF helper. This means that the
> bpf_clear_redirect_map() function can be removed. The actual map item
> is RCU protected.
> 
> The bpf_redirect_info flags member is not used by XDP, and not
> read/written any more. The map member is only written to when
> required/used, and not unconditionally.
> 
> v1->v2 : Removed warning when CONFIG_BPF_SYSCALL was not set. (lkp)
>        : Cleaned up case-clause in xdp_do_generic_redirect_map(). (Toke)
> rfc->v1: Use map_id, and remove bpf_clear_redirect_map(). (Toke)
> 
> Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>
> Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---
>  include/linux/bpf.h        |   1 +
>  include/linux/filter.h     |  11 ++-
>  include/trace/events/xdp.h |  66 +++++++++------
>  kernel/bpf/cpumap.c        |   1 -
>  kernel/bpf/devmap.c        |   1 -
>  net/core/filter.c          | 165 ++++++++++++++++---------------------
>  net/xdp/xskmap.c           |   1 -
>  7 files changed, 122 insertions(+), 124 deletions(-)

I like it! :-)

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

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer