Commit a715dea3 authored Mar 27, 2011 by Anton Blanchard Committed by David S. Miller Mar 28, 2011

net: Always allocate at least 16 skb frags regardless of page size



When analysing performance of the cxgb3 on a ppc64 box I noticed that
we weren't doing much GRO merging. It turns out we are limited by the
number of SKB frags:

#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 2)

With a 4kB page size we have 18 frags, but with a 64kB page size we
only have 3 frags.

I ran a single stream TCP bandwidth test to compare the performance of

Signed-off-by: David S. Miller <davem@davemloft.net>

parent 4910ac6c

include/linux/skbuff.h

+7 −1

Original line number	Diff line number	Diff line
		@@ -122,8 +122,14 @@ struct sk_buff_head {

		struct sk_buff;

		/* To allow 64K frame to be packed as single skb without frag_list */
		/* To allow 64K frame to be packed as single skb without frag_list. Since
		* GRO uses frags we allocate at least 16 regardless of page size.
		*/
		#if (65536/PAGE_SIZE + 2) < 16
		#define MAX_SKB_FRAGS 16
		#else
		#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 2)
		#endif

		typedef struct skb_frag_struct skb_frag_t;