sctp: Allow to disable SCTP checksums via module parameter

This is a new version of my patch, now using a module parameter instead
of a sysctl, so that the option is harder to find. Please note that,
once the module is loaded, it is still possible to change the value of
the parameter in /sys/module/sctp/parameters/, which is useful if you
want to do performance comparisons without rebooting.

Computation of SCTP checksums significantly affects the performance of
SCTP. For example, using two dual-Opteron 246 connected using a Gbe
network, it was not possible to achieve more than ~730 Mbps, compared to
941 Mbps after disabling SCTP checksums.
Unfortunately, SCTP checksum offloading in NICs is not commonly
available (yet).

By default, checksums are still enabled, of course.

Signed-off-by: Lucas Nussbaum <[e-mail]>
Signed-off-by: Vlad Yasevich <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/sctp/structs.h

···
 
 	/* Flag to idicate if SCTP-AUTH is enabled */
 	int auth_enable;
+
+	/* Flag to indicate whether computing and verifying checksum
+	 * is disabled. */
+        int checksum_disable;
 } sctp_globals;
 
 #define sctp_rto_initial		(sctp_globals.rto_initial)
···
 #define sctp_addip_noauth		(sctp_globals.addip_noauth_enable)
 #define sctp_prsctp_enable		(sctp_globals.prsctp_enable)
 #define sctp_auth_enable		(sctp_globals.auth_enable)
+#define sctp_checksum_disable		(sctp_globals.checksum_disable)
 
 /* SCTP Socket type: UDP or TCP style. */
 typedef enum {

net/sctp/input.c

···
 	__skb_pull(skb, skb_transport_offset(skb));
 	if (skb->len < sizeof(struct sctphdr))
 		goto discard_it;
-	if (!skb_csum_unnecessary(skb) && sctp_rcv_checksum(skb) < 0)
+	if (!sctp_checksum_disable && !skb_csum_unnecessary(skb) &&
+		  sctp_rcv_checksum(skb) < 0)
 		goto discard_it;
 
 	skb_pull(skb, sizeof(struct sctphdr));

net/sctp/output.c

···
 	 * Note: Adler-32 is no longer applicable, as has been replaced
 	 * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
 	 */
-	if (!(dst->dev->features & NETIF_F_NO_CSUM)) {
+	if (!sctp_checksum_disable && !(dst->dev->features & NETIF_F_NO_CSUM)) {
 		crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
 		crc32 = sctp_end_cksum(crc32);
 	} else

net/sctp/protocol.c

···
 MODULE_ALIAS("net-pf-" __stringify(PF_INET6) "-proto-132");
 MODULE_AUTHOR("Linux Kernel SCTP developers <[e-mail]>");
 MODULE_DESCRIPTION("Support for the SCTP protocol (RFC2960)");
+module_param_named(no_checksums, sctp_checksum_disable, bool, 0644);
+MODULE_PARM_DESC(no_checksums, "Disable checksums computing and verification");
 MODULE_LICENSE("GPL");