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Commit 4947d3ef authored by Benjamin LaHaise's avatar Benjamin LaHaise Committed by David S. Miller
Browse files

[NET]: Speed up __alloc_skb() 



From: Benjamin LaHaise <bcrl@kvack.org>

In __alloc_skb(), the use of skb_shinfo() which casts a u8 * to the 
shared info structure results in gcc being forced to do a reload of the 
pointer since it has no information on possible aliasing.  Fix this by 
using a pointer to refer to skb_shared_info.

By initializing skb_shared_info sequentially, the write combining buffers 
can reduce the number of memory transactions to a single write.  Reorder 
the initialization in __alloc_skb() to match the structure definition.  
There is also an alignment issue on 64 bit systems with skb_shared_info 
by converting nr_frags to a short everything packs up nicely.

Also, pass the slab cache pointer according to the fclone flag instead 
of using two almost identical function calls.

This raises bw_unix performance up to a peak of 707KB/s when combined 
with the spinlock patch.  It should help other networking protocols, too.

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 17ba15fb

include/linux/skbuff.h

+1 −1
Original line number Diff line number Diff line
@@ -133,7 +133,7 @@ struct skb_frag_struct { 
 */

struct skb_shared_info {

	atomic_t	dataref;

	unsigned int	nr_frags;

	unsigned short	nr_frags;

	unsigned short	tso_size;

	unsigned short	tso_segs;

	unsigned short  ufo_size;

net/core/skbuff.c

+13 −14
Original line number Diff line number Diff line
@@ -135,17 +135,13 @@ void skb_under_panic(struct sk_buff *skb, int sz, void *here) 
struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,

			    int fclone)

{

	struct skb_shared_info *shinfo;

	struct sk_buff *skb;

	u8 *data;



	/* Get the HEAD */

	if (fclone)

		skb = kmem_cache_alloc(skbuff_fclone_cache,

	skb = kmem_cache_alloc(fclone ? skbuff_fclone_cache : skbuff_head_cache,

				gfp_mask & ~__GFP_DMA);

	else

		skb = kmem_cache_alloc(skbuff_head_cache,

				       gfp_mask & ~__GFP_DMA);



	if (!skb)

		goto out;
@@ -162,6 +158,16 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, 
	skb->data = data;

	skb->tail = data;

	skb->end  = data + size;

	/* make sure we initialize shinfo sequentially */

	shinfo = skb_shinfo(skb);

	atomic_set(&shinfo->dataref, 1);

	shinfo->nr_frags  = 0;

	shinfo->tso_size = 0;

	shinfo->tso_segs = 0;

	shinfo->ufo_size = 0;

	shinfo->ip6_frag_id = 0;

	shinfo->frag_list = NULL;



	if (fclone) {

		struct sk_buff *child = skb + 1;

		atomic_t *fclone_ref = (atomic_t *) (child + 1);
@@ -171,13 +177,6 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, 


		child->fclone = SKB_FCLONE_UNAVAILABLE;

	}

	atomic_set(&(skb_shinfo(skb)->dataref), 1);

	skb_shinfo(skb)->nr_frags  = 0;

	skb_shinfo(skb)->tso_size = 0;

	skb_shinfo(skb)->tso_segs = 0;

	skb_shinfo(skb)->frag_list = NULL;

	skb_shinfo(skb)->ufo_size = 0;

	skb_shinfo(skb)->ip6_frag_id = 0;

out:

	return skb;

nodata: