svn commit: r189863 - in head: share/man/man4 sys/net

[Robert Watson]

Author: rwatson
Date: Sun Mar 15 20:17:44 2009
New Revision: 189863
URL: http://svn.freebsd.org/changeset/base/189863

Log:
  Teach the loopback interface about checksum generation and validation
  avoidance:
  
  - Enable setting the RXCSUM and TXCSUM flags for loopback interfaces;
    set both by default.
  - When RXCSUM is set, flag packets sent over the loopback interface as
    having checked and valid IP, UDP, TCP checksums so that higher
    protocol layers won't check them.
  - Always clear CSUM_{IP,UDP_TCP} checksum required flags on transmit,
    as they will have gotten there as a result of TXCSUM being set.
  
  This is done only for packets explicitly sent over the loopback, not
  simulated loopback via if_simloop() due to !SIMPLEX interfaces, etc.
  
  Note that enabling TXCSUM but not RXCSUM will lead to unhappiness, as
  checksums won't be generated but will be validated.
  
  Kris reports that this leads to significant performance improvements
  in loopback benchmarking with TCP and UDP for throughput:
  
  	RXCSUM 	RXCSUM+TXCSUM
  TCP	15%	37%
  UDP	10%	74%
  
  Update man page.
  
  Reviewed by:	sam
  Tested by:	kris
  MFC after:	1 week

Modified:
  head/share/man/man4/lo.4
  head/sys/net/if_loop.c

Modified: head/share/man/man4/lo.4
==============================================================================
--- head/share/man/man4/lo.4	Sun Mar 15 19:38:34 2009	(r189862)
+++ head/share/man/man4/lo.4	Sun Mar 15 20:17:44 2009	(r189863)
@@ -1,5 +1,7 @@
 .\" Copyright (c) 1983, 1991, 1993
-.\"	The Regents of the University of California.  All rights reserved.
+.\"	The Regents of the University of California.
+.\" Copyright (c) 2009 Robert N. M. Watson
+.\" All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
@@ -9,10 +11,6 @@
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
-.\" 3. All advertising materials mentioning features or use of this software
-.\"    must display the following acknowledgement:
-.\"	This product includes software developed by the University of
-.\"	California, Berkeley and its contributors.
 .\" 4. Neither the name of the University nor the names of its contributors
 .\"    may be used to endorse or promote products derived from this software
 .\"    without specific prior written permission.
@@ -32,7 +30,7 @@
 .\"     @(#)lo.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd June 5, 1993
+.Dd March 15, 2009
 .Dt LO 4
 .Os
 .Sh NAME
@@ -58,6 +56,20 @@ The loopback should
 .Em never
 be configured first unless no hardware
 interfaces exist.
+.Pp
+If the transmit checksum offload capability flag is enabled on a loopback
+interface, checksums will not be generated by IP, UDP, or TCP for packets
+sent on the interface.
+.Pp
+If the receive checksum offload capability flag is enabled on a loopback
+interface, checksums will not be validated by IP, UDP, or TCP for packets
+received on the interface.
+.Pp
+By default, both receive and transmit checksum flags will be enabled, in
+order to avoid the overhead of checksumming for local communication where
+data corruption is unlikely.
+If transmit checksum generation is disabled, then validation should also be
+disabled in order to avoid packets being dropped due to invalid checksums.
 .Sh DIAGNOSTICS
 .Bl -diag
 .It lo%d: can't handle af%d.
@@ -74,8 +86,5 @@ The
 .Nm
 device appeared in
 .Bx 4.2 .
-.Sh BUGS
-Previous versions of the system enabled the loopback interface
-automatically, using a nonstandard Internet address (127.1).
-Use of that address is now discouraged; a reserved host address
-for the local network should be used instead.
+The current checksum generation and validation avoidance policy appeared in
+.Fx 8.0 .

Modified: head/sys/net/if_loop.c
==============================================================================
--- head/sys/net/if_loop.c	Sun Mar 15 19:38:34 2009	(r189862)
+++ head/sys/net/if_loop.c	Sun Mar 15 20:17:44 2009	(r189863)
@@ -138,6 +138,8 @@ lo_clone_create(struct if_clone *ifc, in
 	ifp->if_ioctl = loioctl;
 	ifp->if_output = looutput;
 	ifp->if_snd.ifq_maxlen = ifqmaxlen;
+	ifp->if_hwassist = ifp->if_capabilities = ifp->if_capenable =
+	    IFCAP_HWCSUM;
 	if_attach(ifp);
 	bpfattach(ifp, DLT_NULL, sizeof(u_int32_t));
 	if (V_loif == NULL)
@@ -212,6 +214,13 @@ looutput(struct ifnet *ifp, struct mbuf 
 #if 1	/* XXX */
 	switch (dst->sa_family) {
 	case AF_INET:
+		if (ifp->if_capenable & IFCAP_RXCSUM) {
+			m->m_pkthdr.csum_data = 0xffff;
+			m->m_pkthdr.csum_flags = CSUM_DATA_VALID |
+			    CSUM_PSEUDO_HDR | CSUM_IP_CHECKED |
+			    CSUM_IP_VALID | CSUM_SCTP_VALID;
+		}
+		m->m_pkthdr.csum_flags &= ~(CSUM_IP | CSUM_TCP | CSUM_UDP);
 	case AF_INET6:
 	case AF_IPX:
 	case AF_APPLETALK:
@@ -348,7 +357,7 @@ loioctl(struct ifnet *ifp, u_long cmd, c
 {
 	struct ifaddr *ifa;
 	struct ifreq *ifr = (struct ifreq *)data;
-	int error = 0;
+	int error = 0, mask;
 
 	switch (cmd) {
 	case SIOCSIFADDR:
@@ -391,6 +400,18 @@ loioctl(struct ifnet *ifp, u_long cmd, c
 	case SIOCSIFFLAGS:
 		break;
 
+	case SIOCSIFCAP:
+		mask = ifp->if_capenable ^ ifr->ifr_reqcap;
+		if ((mask & IFCAP_RXCSUM) != 0)
+			ifp->if_capenable ^= IFCAP_RXCSUM;
+		if ((mask & IFCAP_TXCSUM) != 0)
+			ifp->if_capenable ^= IFCAP_TXCSUM;
+		if (ifp->if_capenable & IFCAP_TXCSUM)
+			ifp->if_hwassist = CSUM_IP | CSUM_TCP | CSUM_UDP;
+		else
+			ifp->if_hwassist = 0;
+		break;
+
 	default:
 		error = EINVAL;
 	}