[NETFILTER]: xt_hashlimit: speedup hash_dst()
1) Using jhash2() instead of jhash() is a litle bit faster if applicable.
2) Thanks to jhash, hash value uses full 32 bits.
Instead of returning hash % size (implying a divide)
we return the high 32 bits of the (hash * size) that will
give results between [0 and size-1] and same hash distribution.
On most cpus, a multiply is less expensive than a divide, by an order
of magnitude.
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Signed-off-by: Patrick McHardy <kaber@xxxxxxxxx>
---
commit 990af8a278165f0bf91b6d13d9caa61260633868
tree 3804d1bb66fe40adf69e2cd4ef425079fd007b99
parent 561162888ca9bb1ca4a95c41e7d4e03aae0d79c7
author Eric Dumazet <dada1@xxxxxxxxxxxxx> Mon, 17 Dec 2007 14:58:57 +0100
committer Patrick McHardy <kaber@xxxxxxxxx> Tue, 18 Dec 2007 00:25:00 +0100
net/netfilter/xt_hashlimit.c | 11 ++++++++++-
1 files changed, 10 insertions(+), 1 deletions(-)
diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 951d4c8..651c1d2 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -105,7 +105,16 @@ static inline bool dst_cmp(const struct dsthash_ent *ent,
static u_int32_t
hash_dst(const struct xt_hashlimit_htable *ht, const struct dsthash_dst *dst)
{
- return jhash(dst, sizeof(*dst), ht->rnd) % ht->cfg.size;
+ u_int32_t hash = jhash2((const u32 *)dst,
+ sizeof(*dst)/sizeof(u32),
+ ht->rnd);
+ /*
+ * Instead of returning hash % ht->cfg.size (implying a divide)
+ * we return the high 32 bits of the (hash * ht->cfg.size) that will
+ * give results between [0 and cfg.size-1] and same hash distribution,
+ * but using a multiply, less expensive than a divide
+ */
+ return ((u64)hash * ht->cfg.size) >> 32;
}
static struct dsthash_ent *
-
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