netdev - Re: [PATCH v2 bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE

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Date:   Mon, 11 Nov 2019 16:40:29 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andriin@...com>
CC:     bpf <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii.nakryiko@...il.com" <andrii.nakryiko@...il.com>,
        Kernel Team <Kernel-team@...com>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: add mmap() support for
 BPF_MAP_TYPE_ARRAY



> On Nov 9, 2019, at 12:06 AM, Andrii Nakryiko <andriin@...com> wrote:
> 
> Add ability to memory-map contents of BPF array map. This is extremely useful
> for working with BPF global data from userspace programs. It allows to avoid
> typical bpf_map_{lookup,update}_elem operations, improving both performance
> and usability.

[...]

> 
> Generated code for memory-mapped array:
> 
> ; p = bpf_map_lookup_elem(&data_map, &zero);
>  22: (18) r1 = map[id:27]
>  24: (07) r1 += 400			/* array->data offset */
>  25: (79) r1 = *(u64 *)(r1 +0)		/* extra dereference */
>  26: (61) r0 = *(u32 *)(r2 +0)
>  27: (35) if r0 >= 0x3 goto pc+3
>  28: (67) r0 <<= 3
>  29: (0f) r0 += r1
>  30: (05) goto pc+1
>  31: (b7) r0 = 0
> 
> Cc: Rik van Riel <riel@...riel.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Acked-by: Song Liu <songliubraving@...com>