RE: [PATCH v2 bpf-next 4/4] bpf: inline bpf_map_lookup_elem() helper for PERCPU_HASH map

[John Fastabend <john.fastabend@gmail.com>]

Andrii Nakryiko wrote:
> Using new per-CPU BPF instruction, partially inline
> bpf_map_lookup_elem() helper for per-CPU hashmap BPF map. Just like for
> normal HASH map, we still generate a call into __htab_map_lookup_elem(),
> but after that we resolve per-CPU element address using a new
> instruction, saving on extra functions calls.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  kernel/bpf/hashtab.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index e81059faae63..83a9a74260e9 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -2308,6 +2308,26 @@ static void *htab_percpu_map_lookup_elem(struct bpf_map *map, void *key)
>  		return NULL;
>  }
>  
> +/* inline bpf_map_lookup_elem() call for per-CPU hashmap */
> +static int htab_percpu_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
> +{
> +	struct bpf_insn *insn = insn_buf;
> +
> +	if (!bpf_jit_supports_percpu_insn())
> +		return -EOPNOTSUPP;
> +
> +	BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
> +		     (void *(*)(struct bpf_map *map, void *key))NULL));
> +	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
> +	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 3);
> +	*insn++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_0,
> +				offsetof(struct htab_elem, key) + map->key_size);
> +	*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +	*insn++ = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> +
> +	return insn - insn_buf;
> +}
> +
>  static void *htab_percpu_map_lookup_percpu_elem(struct bpf_map *map, void *key, u32 cpu)
>  {
>  	struct htab_elem *l;
> @@ -2436,6 +2456,7 @@ const struct bpf_map_ops htab_percpu_map_ops = {
>  	.map_free = htab_map_free,
>  	.map_get_next_key = htab_map_get_next_key,
>  	.map_lookup_elem = htab_percpu_map_lookup_elem,
> +	.map_gen_lookup = htab_percpu_map_gen_lookup,
>  	.map_lookup_and_delete_elem = htab_percpu_map_lookup_and_delete_elem,
>  	.map_update_elem = htab_percpu_map_update_elem,
>  	.map_delete_elem = htab_map_delete_elem,


Thanks I'll test on Tetragon as well to see if we can see some perf improvement we have
a few per cpu maps int here as well.

Acked-by: John Fastabend <john.fastabend@gmail.com>