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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: Anton Protopopov <aspsk@isovalent.com>
Link: https://lore.kernel.org/r/20230402114340.3441-1-aspsk@isovalent.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Anton Protopopov 2023-04-02 11:43:40 +00:00 committed by Alexei Starovoitov
parent 5b85575ad4
commit 92b2e810f0
1 changed files with 2 additions and 15 deletions
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17
kernel/bpf/bloom_filter.c
View File

@ -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();