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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>
This commit is contained in:
Anton Blanchard 2011-03-27 14:57:26 +00:00 committed by David S. Miller
parent 4910ac6c52
commit a715dea3c8
1 changed files with 7 additions and 1 deletions
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8
include/linux/skbuff.h
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@ -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;