NOTES on debugging netmap performance

/*
 * debugging support to analyse syscall behaviour
 *	netmap_drop is the point where to drop

	Path is:

	./libthr/thread/thr_syscalls.c
	lib/libc/i386/SYS.h
	lib/libc/i386/sys/syscall.S

	head/sys/kern/syscall.master
	; Processed to created init_sysent.c, syscalls.c and syscall.h.
	sys/kern/uipc_syscalls.c::sys_sendto()
		sendit()
		kern_sendit()
		sosend()
	sys/kern/uipc_socket.c::sosend()
		so->so_proto->pr_usrreqs->pru_sosend(...)
	sys/netinet/udp_usrreq.c::udp_usrreqs { }
		.pru_sosend =           sosend_dgram,
		.pru_send =             udp_send,
		.pru_soreceive =        soreceive_dgram,
	sys/kern/uipc_socket.c::sosend_dgram()
		m_uiotombuf()
		(*so->so_proto->pr_usrreqs->pru_send)
	sys/netinet/udp_usrreq.c::udp_send()
		sotoinpcb(so);
		udp_output()
			INP_RLOCK(inp);
			INP_HASH_RLOCK(&V_udbinfo);
		fill udp and ip headers
		ip_output()

	30	udp_send() before udp_output	
	31	udp_output before ip_output
	32	udp_output beginning
	33	before in_pcbbind_setup
	34	after in_pcbbind_setup
	35	before prison_remote_ip4
	36	after prison_remote_ip4
	37	before computing udp

	20	beginning of sys_sendto
	21	beginning of sendit
	22	sendit after getsockaddr
	23	before kern_sendit
	24	kern_sendit before getsock_cap()
	25	kern_sendit before sosend()

	40	sosend_dgram beginning
	41	sosend_dgram after sbspace
	42	sosend_dgram after m_uiotombuf
	43	sosend_dgram after SO_DONTROUTE
	44	sosend_dgram after pru_send (useless)

	50	ip_output beginning
	51	ip_output after flowtable
	52	ip_output at sendit
	53	ip_output after pfil_hooked
	54	ip_output at passout
	55	ip_output before if_output
	56	ip_output after rtalloc etc.

	60	uiomove print

	70	pfil.c:: pfil_run_hooks beginning
	71	print number of pfil entries

	80	ether_output start
	81	ether_output after first switch
	82	ether_output after M_PREPEND
	83	ether_output after simloop
	84	ether_output after carp and netgraph
	85	ether_output_frame before if_transmit()

	90	ixgbe_mq_start (if_transmit) beginning
	91	ixgbe_mq_start_locked before ixgbe_xmit

FLAGS:
	1	disable ETHER_BPF_MTAP
	2	disable drbr stats update
	4
	8
	16
	32
	64
	128
 */
