pppoe: optimize hash with word access

Currently, hash_item() processes the 6-byte Ethernet address and the
2-byte session ID byte-wise to compute a hash.

Optimize this by using 16-bit word operations: XOR three 16-bit words
from the Ethernet address and the 16-bit session ID, then fold the
result. This reduces the total number of loads and XORs. The Ethernet
addresses in a skb and struct pppoe_addr are both 2-byte aligned, so the
u16 pointer cast is safe.

Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
Link: https://patch.msgid.link/20260429023848.153425-1-qingfang.deng@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
index bdd61c504a1c4565aa43b6e5793fa6439b88245f..ad5bb98c15794b9d02b207531f404cc23158d693 100644 (file)
--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -136,15 +136,15 @@ static inline int cmp_addr(struct pppoe_addr *a, __be16 sid, char *addr)
 #error 8 must be a multiple of PPPOE_HASH_BITS
 #endif
 
-static int hash_item(__be16 sid, unsigned char *addr)
+static u8 hash_item(__be16 sid, const u8 addr[ETH_ALEN])
 {
-       unsigned char hash = 0;
+       const u16 *addr16 = (const u16 *)addr;
        unsigned int i;
+       u16 hash16;
+       u8 hash;
 
-       for (i = 0; i < ETH_ALEN; i++)
-               hash ^= addr[i];
-       for (i = 0; i < sizeof(sid_t) * 8; i += 8)
-               hash ^= (__force __u32)sid >> i;
+       hash16 = addr16[0] ^ addr16[1] ^ addr16[2] ^ (__force u16)sid;
+       hash = (hash16 >> 8) ^ hash16;
        for (i = 8; (i >>= 1) >= PPPOE_HASH_BITS;)
                hash ^= hash >> i;