tcp: makes tcp_try_coalesce aware of skb->head_frag
authorEric Dumazet <edumazet@google.com>
Fri, 27 Apr 2012 00:38:33 +0000 (00:38 +0000)
committerDavid S. Miller <davem@davemloft.net>
Tue, 1 May 2012 01:35:49 +0000 (21:35 -0400)
commit329033f645d93b5f9160b9b972dbc5431ad22a33
tree1fca09d6bf496391b8ea5d109429e48b28b2d7a8
parentd7e8883cfcf4851afe74fb380cc62b7fa9cf66ba
tcp: makes tcp_try_coalesce aware of skb->head_frag

TCP coalesce can check if skb to be merged has its skb->head mapped to a
page fragment, instead of a kmalloc() area.

We had to disable coalescing in this case, for performance reasons.

We 'upgrade' skb->head as a fragment in itself.

This reduces number of cache misses when user makes its copies, since a
less sk_buff are fetched.

This makes receive and ofo queues shorter and thus reduce cache line
misses in TCP stack.

This is a followup of patch "net: allow skb->head to be a page fragment"

Tested with tg3 nic, with GRO on or off. We can see "TCPRcvCoalesce"
counter being incremented.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Matt Carlson <mcarlson@broadcom.com>
Cc: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
net/ipv4/tcp_input.c