[RFC PATCH bpf-next 14/14] bpf, hashtab: Compare keys in long

[Toshiaki Makita <toshiaki.makita1@gmail.com>]

memcmp() is generally slow. Compare keys in long if possible.
This improves xdp_flow performance.
This is included in this series just to demonstrate to what extent
xdp_flow performance can increase.

Signed-off-by: Toshiaki Makita <toshiaki.makita1@gmail.com>
---
 kernel/bpf/hashtab.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 22066a6..8b5ffd4 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -417,6 +417,29 @@ static inline struct hlist_nulls_head *select_bucket(struct bpf_htab *htab, u32
 	return &__select_bucket(htab, hash)->head;
 }
 
+/* key1 must be aligned to sizeof long */
+static bool key_equal(void *key1, void *key2, u32 size)
+{
+	/* Check for key1 */
+	BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct htab_elem, key),
+				 sizeof(long)));
+
+	if (IS_ALIGNED((unsigned long)key2 | (unsigned long)size,
+		       sizeof(long))) {
+		unsigned long *lkey1, *lkey2;
+
+		for (lkey1 = key1, lkey2 = key2; size > 0;
+		     lkey1++, lkey2++, size -= sizeof(long)) {
+			if (*lkey1 != *lkey2)
+				return false;
+		}
+
+		return true;
+	}
+
+	return !memcmp(key1, key2, size);
+}
+
 /* this lookup function can only be called with bucket lock taken */
 static struct htab_elem *lookup_elem_raw(struct hlist_nulls_head *head, u32 hash,
 					 void *key, u32 key_size)
@@ -425,7 +448,7 @@ static struct htab_elem *lookup_elem_raw(struct hlist_nulls_head *head, u32 hash
 	struct htab_elem *l;
 
 	hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
-		if (l->hash == hash && !memcmp(&l->key, key, key_size))
+		if (l->hash == hash && key_equal(&l->key, key, key_size))
 			return l;
 
 	return NULL;
@@ -444,7 +467,7 @@ static struct htab_elem *lookup_nulls_elem_raw(struct hlist_nulls_head *head,
 
 again:
 	hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
-		if (l->hash == hash && !memcmp(&l->key, key, key_size))
+		if (l->hash == hash && key_equal(&l->key, key, key_size))
 			return l;
 
 	if (unlikely(get_nulls_value(n) != (hash & (n_buckets - 1))))
-- 
1.8.3.1