| Message ID | 20120505002645.21292.38368.stgit@gitlad.jf.intel.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Fri, 2012-05-04 at 17:26 -0700, Alexander Duyck wrote: > The fast-path for pskb_expand_head contains a check where the size plus the > unaligned size of skb_shared_info is compared against the size of the data > buffer. This code path has two issues. First is the fact that after the > recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info > is always placed in the optimal spot for a buffer size making this check > unnecessary. The second issue is the fact that the check doesn't take into > account the aligned size of shared info. As a result the code burns cycles > doing a memcpy with nothing actually being shifted. > > Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com> > --- > > net/core/skbuff.c | 12 ------------ > 1 files changed, 0 insertions(+), 12 deletions(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index c199aa4..4d085d4 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -951,17 +951,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta; > } > > - if (fastpath && !skb->head_frag && > - size + sizeof(struct skb_shared_info) <= ksize(skb->head)) { > - memmove(skb->head + size, skb_shinfo(skb), > - offsetof(struct skb_shared_info, > - frags[skb_shinfo(skb)->nr_frags])); > - memmove(skb->head + nhead, skb->head, > - skb_tail_pointer(skb) - skb->head); > - off = nhead; > - goto adjust_others; > - } > - > data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), > gfp_mask); > if (!data) > @@ -997,7 +986,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > > skb->head = data; > skb->head_frag = 0; > -adjust_others: > skb->data += off; > #ifdef NET_SKBUFF_DATA_USES_OFFSET > skb->end = size; > I totally agree this code is no longer needed, we already have the skb_shared_info at the end of the buffer. Acked-by: Eric Dumazet <edumazet@google.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Sat, 05 May 2012 07:35:30 +0200 > On Fri, 2012-05-04 at 17:26 -0700, Alexander Duyck wrote: >> The fast-path for pskb_expand_head contains a check where the size plus the >> unaligned size of skb_shared_info is compared against the size of the data >> buffer. This code path has two issues. First is the fact that after the >> recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info >> is always placed in the optimal spot for a buffer size making this check >> unnecessary. The second issue is the fact that the check doesn't take into >> account the aligned size of shared info. As a result the code burns cycles >> doing a memcpy with nothing actually being shifted. >> >> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com> ... > Acked-by: Eric Dumazet <edumazet@google.com> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index c199aa4..4d085d4 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -951,17 +951,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta; } - if (fastpath && !skb->head_frag && - size + sizeof(struct skb_shared_info) <= ksize(skb->head)) { - memmove(skb->head + size, skb_shinfo(skb), - offsetof(struct skb_shared_info, - frags[skb_shinfo(skb)->nr_frags])); - memmove(skb->head + nhead, skb->head, - skb_tail_pointer(skb) - skb->head); - off = nhead; - goto adjust_others; - } - data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), gfp_mask); if (!data) @@ -997,7 +986,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, skb->head = data; skb->head_frag = 0; -adjust_others: skb->data += off; #ifdef NET_SKBUFF_DATA_USES_OFFSET skb->end = size;
The fast-path for pskb_expand_head contains a check where the size plus the unaligned size of skb_shared_info is compared against the size of the data buffer. This code path has two issues. First is the fact that after the recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info is always placed in the optimal spot for a buffer size making this check unnecessary. The second issue is the fact that the check doesn't take into account the aligned size of shared info. As a result the code burns cycles doing a memcpy with nothing actually being shifted. Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com> --- net/core/skbuff.c | 12 ------------ 1 files changed, 0 insertions(+), 12 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html