[PATCH 05/10] net: move destructor_arg to the front of sk_buff.
From: Ian Campbell <hidden>
Date: 2012-04-10 14:32:39
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
As of the previous patch we align the end (rather than the start) of the struct to a cache line and so, with 32 and 64 byte cache lines and the shinfo size increase from the next patch, the first 8 bytes of the struct end up on a different cache line to the rest of it so make sure it is something relatively unimportant to avoid hitting an extra cache line on hot operations such as kfree_skb. Signed-off-by: Ian Campbell <redacted> Cc: "David S. Miller" <davem@davemloft.net> Cc: Eric Dumazet <redacted> --- include/linux/skbuff.h | 15 ++++++++++----- net/core/skbuff.c | 5 ++++- 2 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 0ad6a46..f0ae39c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h@@ -265,6 +265,15 @@ struct ubuf_info { * the end of the header data, ie. at skb->end. */ struct skb_shared_info { + /* Intermediate layers must ensure that destructor_arg + * remains valid until skb destructor */ + void *destructor_arg; + + /* + * Warning: all fields from here until dataref are cleared in + * __alloc_skb() + * + */ unsigned char nr_frags; __u8 tx_flags; unsigned short gso_size;
@@ -276,14 +285,10 @@ struct skb_shared_info { __be32 ip6_frag_id; /* - * Warning : all fields before dataref are cleared in __alloc_skb() + * Warning: all fields before dataref are cleared in __alloc_skb() */ atomic_t dataref; - /* Intermediate layers must ensure that destructor_arg - * remains valid until skb destructor */ - void * destructor_arg; - /* must be last field, see pskb_expand_head() */ skb_frag_t frags[MAX_SKB_FRAGS]; };
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d4e139e..b8a41d6 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c@@ -214,7 +214,10 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, /* make sure we initialize shinfo sequentially */ shinfo = skb_shinfo(skb); - memset(shinfo, 0, offsetof(struct skb_shared_info, dataref)); + + memset(&shinfo->nr_frags, 0, + offsetof(struct skb_shared_info, dataref) + - offsetof(struct skb_shared_info, nr_frags)); atomic_set(&shinfo->dataref, 1); kmemcheck_annotate_variable(shinfo->destructor_arg);
--
1.7.2.5