Re: [PATCH] member: fix PRNG seed reset in NitroSketch mode

[Thomas Monjalon <thomas@monjalon.net>]

Any comment?

20/06/2023 23:17, Dmitry Kozlyuk:
> Sketch creation seeded the global PRNG
> using the supplied seed for hashing.
> The use of this seed by SKETCH set summary was not documented.
> SKETCH set summary does not require two independent hash seeds,
> unlike other set summary types.
> Seeding the global PRNG at sketch creation
> does not make the sketch operation deterministic:
> it uses rte_rand() later, the PRNG may be seeded again by that point.
> On the other hand, seeding the global PRNG with a hash seed,
> is likely undesired, because it may be low-entropy or even constant.
> Deterministic operation can be achieved by seeding the PRNG externally.
> 
> Remove the call to rte_srand() at sketch creation.
> Document that hash seeds are not used by SKETCH set summary type.
> 
> Fixes: db354bd2e1f8 ("member: add NitroSketch mode")
> Cc: leyi.rong@intel.com
> 
> Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
> ---
>  lib/member/rte_member.h        | 1 +
>  lib/member/rte_member_sketch.c | 1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/member/rte_member.h b/lib/member/rte_member.h
> index 072a253c89..d08b143e51 100644
> --- a/lib/member/rte_member.h
> +++ b/lib/member/rte_member.h
> @@ -314,6 +314,7 @@ struct rte_member_parameters {
>  	 * for bucket location.
>  	 * For vBF type, these two hashes and their combinations are used as
>  	 * hash locations to index the bit array.
> +	 * For Sketch type, these seeds are not used.
>  	 */
>  	uint32_t prim_hash_seed;
>  
> diff --git a/lib/member/rte_member_sketch.c b/lib/member/rte_member_sketch.c
> index 524ba77620..d5f35aabe9 100644
> --- a/lib/member/rte_member_sketch.c
> +++ b/lib/member/rte_member_sketch.c
> @@ -227,7 +227,6 @@ rte_member_create_sketch(struct rte_member_setsum *ss,
>  		goto error_runtime;
>  	}
>  
> -	rte_srand(ss->prim_hash_seed);
>  	for (i = 0; i < ss->num_row; i++)
>  		ss->hash_seeds[i] = rte_rand();
>  
>