[RFCv4 PATCH 0/2] net: Introduce recvmmsg socket syscall

Hi,

	Nir, can you please test with this patchset and check if latency
numbers improved? They should, I think :-)

	New perf callgraphs here:

http://oops.ghostprotocols.net:81/acme/perf.recvmsg.step2.cg.data.txt.bz2

versus

http://oops.ghostprotocols.net:81/acme/perf.recvmmsg.step2.cg.data.txt.bz2

	Look at what appears now on the radar, its not locking :-)
	
	Or course, I need to do more tests, but it looks promising, please give
it a go and report back here if you can!

- Arnaldo

# Samples: 761074
#
# Overhead   Command             Shared Object  Symbol
# ........  ........  ........................  ......
#
     6.54%  recvmmsg  [kernel]                  [k] skb_set_owner_r
                |
                |--99.43%-- sock_queue_rcv_skb
                |          __udp_queue_rcv_skb
                |          sk_backlog_rcv
                |          release_sock
                |          __sys_recvmmsg
                |          sys_recvmmsg
                |          system_call_fastpath
                |          syscall
                |          |
                |           --12.76%-- main
                |                     __libc_start_main
                |
                 --0.57%-- __udp_queue_rcv_skb
                           sk_backlog_rcv
                           release_sock
                           __sys_recvmmsg
                           sys_recvmmsg
                           system_call_fastpath
                           syscall
                           |
                            --10.84%-- main
                                      __libc_start_main

     5.88%  recvmmsg  [kernel]                  [k] _spin_lock_irqsave
                |
                |--47.58%-- skb_queue_tail
                |          sock_queue_rcv_skb
                |          __udp_queue_rcv_skb
                |          sk_backlog_rcv
                |          release_sock
                |          __sys_recvmmsg
                |          sys_recvmmsg
                |          system_call_fastpath
                |          syscall
                |          |
                |           --12.56%-- main
                |                     __libc_start_main
                |
                |--41.85%-- __skb_recv_datagram
                |          __udp_recvmsg
                |          udp_unlocked_recvmsg
                |          sock_common_unlocked_recvmsg
                |          __sock_unlocked_recvmsg_nosec
                |          |
                |          |--98.41%-- sock_unlocked_recvmsg_nosec
                |          |          __sys_recvmsg
                |          |          __sys_recvmmsg
                |          |          sys_recvmmsg
                |          |          system_call_fastpath
                |          |          syscall
                |          |          |
                |          |           --12.82%-- main
                |          |                     __libc_start_main
                |          |
                |           --1.59%-- sock_unlocked_recvmsg
                |                     __sys_recvmsg
                |                     __sys_recvmmsg
                |                     sys_recvmmsg


- Arnaldo