Re: [PATCH] hash: add riscv vector support for 16-byte key comparison

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 26 Feb 2026 14:49:38 +0800
P1erreCashon <2022302111412@whu.edu.cn> wrote:

> +/* Functions to compare multiple of 16 byte keys (up to 128 bytes) */
> +static inline int
> +rte_hash_k16_cmp_eq(const void *key1, const void *key2, size_t key_len __rte_unused)
> +{
> +	const uint8_t *p1 = (const uint8_t *)key1;
> +	const uint8_t *p2 = (const uint8_t *)key2;
> +	size_t offset = 0;
> +
> +	while (offset < 16) {
> +		size_t vl = __riscv_vsetvl_e8m1(16 - offset);
> +
> +		vuint8m1_t v1 = __riscv_vle8_v_u8m1(p1 + offset, vl);
> +		vuint8m1_t v2 = __riscv_vle8_v_u8m1(p2 + offset, vl);
> +
> +		/* find != bytes */
> +		vbool8_t neq = __riscv_vmsne_vv_u8m1_b8(v1, v2, vl);
> +
> +		/* if any byte mismatches, return not equal */
> +		if (__riscv_vfirst_m_b8(neq, vl) >= 0)
> +			return 1;
> +
> +		offset += vl;
> +	}
> +
> +	/* all bytes equal */
> +	return 0;
> +}
> +

Compiling this with godbolt generates much bigger code than simple 64 bit version.
Is it really faster?


int
rte_hash_k16_cmp_eq(const void *key1, const void *key2, size_t key_len __rte_unused)
{
	const unaligned_uint64_t *k1 = key1;
	const unaligned_uint64_t *k2 = key2;

	return !!((k1[0] ^ k2[0]) | (k1[1] ^ k2[1]));
}


rte_hash_k16_cmp_eq:
        ld      a4,8(a0)
        ld      a5,0(a0)
        ld      a2,0(a1)
        ld      a3,8(a1)
        xor     a0,a5,a2
        xor     a4,a4,a3
        or      a0,a0,a4
        snez    a0,a0
        ret
ricsv_hash_k16_cmp_eq:
        li      a4,0
        li      a6,16
        li      a7,15
.L5:
        sub     a5,a6,a4
        vsetvli a5,a5,e8,m1,ta,ma
        add     a2,a0,a4
        add     a3,a1,a4
        vle8.v  v1,0(a2)
        vle8.v  v2,0(a3)
        add     a4,a4,a5
        vmsne.vv        v1,v1,v2
        vfirst.m        a5,v1
        bge     a5,zero,.L6
        bleu    a4,a7,.L5
        li      a0,0
        ret
.L6:
        li      a0,1
        ret