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.
-ben
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 97f6580..d94a02e 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -134,7 +134,7 @@ 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;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 83fee37..25c4728 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -135,17 +135,13 @@ void skb_under_panic(struct sk_buff *skb
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,
- gfp_mask & ~__GFP_DMA);
- else
- skb = kmem_cache_alloc(skbuff_head_cache,
- gfp_mask & ~__GFP_DMA);
-
+ skb = kmem_cache_alloc(fclone ? skbuff_fclone_cache : skbuff_head_cache,
+ gfp_mask & ~__GFP_DMA);
if (!skb)
goto out;
@@ -162,6 +158,16 @@ struct sk_buff *__alloc_skb(unsigned int
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
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:
--
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