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>

diff --git a/kernel/bpf/bloom_filter.c b/kernel/bpf/bloom_filter.c
index db19784601a7ff11a7f51163e62e001effd7c1c8..540331b610a97fc73409cd127ef39cfc627a7351 100644 (file)
--- a/kernel/bpf/bloom_filter.c
+++ b/kernel/bpf/bloom_filter.c
@@ -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();