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 <lucas.nussbaum@ens-lyon.fr>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index b78e3be..cc0b592 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -1411,4 +1411,6 @@
 MODULE_ALIAS("net-pf-" __stringify(PF_INET6) "-proto-132");
 MODULE_AUTHOR("Linux Kernel SCTP developers <lksctp-developers@lists.sourceforge.net>");
 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");