After skb allocation, initial skb->fclone value is 0 (SKB_FCLONE_UNAVAILABLE) We can replace one RMW sequence with a single OR instruction. movzbl 0x7e(%r13),%eax // skb->fclone = SKB_FCLONE_ORIG; and $0xf3,%al or $0x4,%al mov %al,0x7e(%r13) -> or $0x4,0x7e(%r13) // skb->fclone |= SKB_FCLONE_ORIG; Signed-off-by: Eric Dumazet --- net/core/skbuff.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index f2367818c130bcd3095e9bd78fbc9f9a0ac83d4b..1c2b9ae7bce6457395a82d5bd577a9e125eceb95 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -723,7 +723,14 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, fclones = container_of(skb, struct sk_buff_fclones, skb1); - skb->fclone = SKB_FCLONE_ORIG; + /* skb->fclone is a 2bits field. + * Replace expensive RMW (skb->fclone = SKB_FCLONE_ORIG) + * with a single OR. + */ + BUILD_BUG_ON(SKB_FCLONE_UNAVAILABLE != 0); + DEBUG_NET_WARN_ON_ONCE(skb->fclone != SKB_FCLONE_UNAVAILABLE); + skb->fclone |= SKB_FCLONE_ORIG; + refcount_set(&fclones->fclone_ref, 1); } -- 2.52.0.457.g6b5491de43-goog