Commit 92b2e810 authored by Anton Protopopov's avatar Anton Protopopov Committed by Alexei Starovoitov
Browse files

bpf: compute hashes in bloom filter similar to hashmap 



If the value size in a bloom filter is a multiple of 4, then the jhash2()
function is used to compute hashes. The length parameter of this function
equals to the number of 32-bit words in input. Compute it in the hot path
instead of pre-computing it, as this is translated to one extra shift to
divide the length by four vs. one extra memory load of a pre-computed length.

Signed-off-by: default avatarAnton Protopopov <aspsk@isovalent.com>
Link: https://lore.kernel.org/r/20230402114340.3441-1-aspsk@isovalent.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 5b85575a

kernel/bpf/bloom_filter.c

+2 −15
Original line number Diff line number Diff line
@@ -16,13 +16,6 @@ struct bpf_bloom_filter { 
	struct bpf_map map;

	u32 bitset_mask;

	u32 hash_seed;

	/* If the size of the values in the bloom filter is u32 aligned,

	 * then it is more performant to use jhash2 as the underlying hash

	 * function, else we use jhash. This tracks the number of u32s

	 * in an u32-aligned value size. If the value size is not u32 aligned,

	 * this will be 0.

	 */

	u32 aligned_u32_count;

	u32 nr_hash_funcs;

	unsigned long bitset[];

};
@@ -32,9 +25,8 @@ static u32 hash(struct bpf_bloom_filter *bloom, void *value, 
{

	u32 h;



	if (bloom->aligned_u32_count)

		h = jhash2(value, bloom->aligned_u32_count,

			   bloom->hash_seed + index);

	if (likely(value_size % 4 == 0))

		h = jhash2(value, value_size / 4, bloom->hash_seed + index);

	else

		h = jhash(value, value_size, bloom->hash_seed + index);
@@ -152,11 +144,6 @@ static struct bpf_map *bloom_map_alloc(union bpf_attr *attr) 
	bloom->nr_hash_funcs = nr_hash_funcs;

	bloom->bitset_mask = bitset_mask;



	/* Check whether the value size is u32-aligned */

	if ((attr->value_size & (sizeof(u32) - 1)) == 0)

		bloom->aligned_u32_count =

			attr->value_size / sizeof(u32);



	if (!(attr->map_flags & BPF_F_ZERO_SEED))

		bloom->hash_seed = get_random_u32();