Commit c2dd4059 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: minor optimization in __alloc_skb() 



TCP allocates 'fast clones' skbs for packets in tx queues.

Currently, __alloc_skb() initializes the companion fclone
field to SKB_FCLONE_CLONE, and leaves other fields untouched.

It makes sense to defer this init much later in skb_clone(),
because all fclone fields are copied and hot in cpu caches
at that time.

This removes one cache line miss in __alloc_skb(), cost seen
on an host with 256 cpus all competing on memory accesses.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8e151457

net/core/skbuff.c

+1 −2
Original line number Diff line number Diff line
@@ -454,8 +454,6 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, 


		skb->fclone = SKB_FCLONE_ORIG;

		refcount_set(&fclones->fclone_ref, 1);



		fclones->skb2.fclone = SKB_FCLONE_CLONE;

	}



	return skb;
@@ -1513,6 +1511,7 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask) 
	    refcount_read(&fclones->fclone_ref) == 1) {

		n = &fclones->skb2;

		refcount_set(&fclones->fclone_ref, 2);

		n->fclone = SKB_FCLONE_CLONE;

	} else {

		if (skb_pfmemalloc(skb))

			gfp_mask |= __GFP_MEMALLOC;