netdev - Re: [PATCH bpf-next v3] libbpf: use implicit XSKMAP lookup from AF

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Message-ID: <87ftjlp703.fsf@toke.dk>
Date:   Tue, 22 Oct 2019 09:35:40 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>,
        netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        bpf@...r.kernel.org, magnus.karlsson@...il.com,
        magnus.karlsson@...el.com, sridhar.samudrala@...el.com
Subject: Re: [PATCH bpf-next v3] libbpf: use implicit XSKMAP lookup from AF_XDP XDP program

Björn Töpel <bjorn.topel@...il.com> writes:

> From: Björn Töpel <bjorn.topel@...el.com>
>
> In commit 43e74c0267a3 ("bpf_xdp_redirect_map: Perform map lookup in
> eBPF helper") the bpf_redirect_map() helper learned to do map lookup,
> which means that the explicit lookup in the XDP program for AF_XDP is
> not needed for post-5.3 kernels.
>
> This commit adds the implicit map lookup with default action, which
> improves the performance for the "rx_drop" [1] scenario with ~4%.
>
> For pre-5.3 kernels, the bpf_redirect_map() returns XDP_ABORTED, and a
> fallback path for backward compatibility is entered, where explicit
> lookup is still performed. This means a slight regression for older
> kernels (an additional bpf_redirect_map() call), but I consider that a
> fair punishment for users not upgrading their kernels. ;-)
>
> v1->v2: Backward compatibility (Toke) [2]
> v2->v3: Avoid masking/zero-extension by using JMP32 [3]
>
> [1] # xdpsock -i eth0 -z -r
> [2] https://lore.kernel.org/bpf/87pnirb3dc.fsf@toke.dk/
> [3] https://lore.kernel.org/bpf/87v9sip0i8.fsf@toke.dk/
>
> Suggested-by: Toke Høiland-Jørgensen <toke@...hat.com>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>

Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>