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authorEric Dumazet <eric.dumazet@gmail.com>2011-11-14 10:03:34 +0400
committerDavid S. Miller <davem@davemloft.net>2011-11-14 23:13:30 +0400
commitb2b5ce9d1ccf1c45f8ac68e5d901112ab76ba199 (patch)
tree60839b87de74c617f417eaccbbac98c770c9fc90 /include/linux/skbuff.h
parentc3e072f8a6c5625028531c40ec65f7e301531be2 (diff)
downloadlinux-b2b5ce9d1ccf1c45f8ac68e5d901112ab76ba199.tar.xz
net: introduce build_skb()
One of the thing we discussed during netdev 2011 conference was the idea to change some network drivers to allocate/populate their skb at RX completion time, right before feeding the skb to network stack. In old days, we allocated skbs when populating the RX ring. This means bringing into cpu cache sk_buff and skb_shared_info cache lines (since we clear/initialize them), then 'queue' skb->data to NIC. By the time NIC fills a frame in skb->data buffer and host can process it, cpu probably threw away the cache lines from its caches, because lot of things happened between the allocation and final use. So the deal would be to allocate only the data buffer for the NIC to populate its RX ring buffer. And use build_skb() at RX completion to attach a data buffer (now filled with an ethernet frame) to a new skb, initialize the skb_shared_info portion, and give the hot skb to network stack. build_skb() is the function to allocate an skb, caller providing the data buffer that should be attached to it. Drivers are expected to call skb_reserve() right after build_skb() to adjust skb->data to the Ethernet frame (usually skipping NET_SKB_PAD and NET_IP_ALIGN, but some drivers might add a hardware provided alignment) Data provided to build_skb() MUST have been allocated by a prior kmalloc() call, with enough room to add SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) bytes at the end of the data without corrupting incoming frame. data = kmalloc(NET_SKB_PAD + NET_IP_ALIGN + 1536 + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), GFP_ATOMIC); ... skb = build_skb(data); if (!skb) { recycle_data(data); } else { skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN); ... } Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> CC: Eilon Greenstein <eilong@broadcom.com> CC: Ben Hutchings <bhutchings@solarflare.com> CC: Tom Herbert <therbert@google.com> CC: Jamal Hadi Salim <hadi@mojatatu.com> CC: Stephen Hemminger <shemminger@vyatta.com> CC: Thomas Graf <tgraf@infradead.org> CC: Herbert Xu <herbert@gondor.apana.org.au> CC: Jeff Kirsher <jeffrey.t.kirsher@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/skbuff.h')
-rw-r--r--include/linux/skbuff.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index fe864885c1ed..abad8a0941e8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -540,6 +540,7 @@ extern void consume_skb(struct sk_buff *skb);
extern void __kfree_skb(struct sk_buff *skb);
extern struct sk_buff *__alloc_skb(unsigned int size,
gfp_t priority, int fclone, int node);
+extern struct sk_buff *build_skb(void *data);
static inline struct sk_buff *alloc_skb(unsigned int size,
gfp_t priority)
{