netdev - Re: [RFC PATCH bpf-next 3/3] bpf, arm64: Optimize ADD,SUB,JMP BPF

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Date:   Thu, 7 May 2020 22:22:07 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Luke Nelson <lukenels@...washington.edu>, bpf@...r.kernel.org
Cc:     Luke Nelson <luke.r.nels@...il.com>, Xi Wang <xi.wang@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Enrico Weigelt <info@...ux.net>, Torsten Duwe <duwe@...e.de>,
        Allison Randal <allison@...utok.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [RFC PATCH bpf-next 3/3] bpf, arm64: Optimize ADD,SUB,JMP BPF_K
 using arm64 add/sub immediates

On 5/7/20 3:05 AM, Luke Nelson wrote:
> The current code for BPF_{ADD,SUB} BPF_K loads the BPF immediate to a
> temporary register before performing the addition/subtraction. Similarly,
> BPF_JMP BPF_K cases load the immediate to a temporary register before
> comparison.
> 
> This patch introduces optimizations that use arm64 immediate add, sub,
> cmn, or cmp instructions when the BPF immediate fits. If the immediate
> does not fit, it falls back to using a temporary register.
> 
> Example of generated code for BPF_ALU64_IMM(BPF_ADD, R0, 2):
> 
> without optimization:
> 
>    24: mov x10, #0x2
>    28: add x7, x7, x10
> 
> with optimization:
> 
>    24: add x7, x7, #0x2
> 
> The code could use A64_{ADD,SUB}_I directly and check if it returns
> AARCH64_BREAK_FAULT, similar to how logical immediates are handled.
> However, aarch64_insn_gen_add_sub_imm from insn.c prints error messages
> when the immediate does not fit, and it's simpler to check if the
> immediate fits ahead of time.
> 
> Co-developed-by: Xi Wang <xi.wang@...il.com>
> Signed-off-by: Xi Wang <xi.wang@...il.com>
> Signed-off-by: Luke Nelson <luke.r.nels@...il.com>

Same here:

Acked-by: Daniel Borkmann <daniel@...earbox.net>

Thanks!