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>

4 files changed, 10 insertions, 2 deletions

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 9661d7b765f0..9f70d54fcefc 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -218,6 +218,10 @@ extern struct sctp_globals {
 
         /* 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)
@@ -252,6 +256,7 @@ extern struct sctp_globals {
 #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 {
diff --git a/net/sctp/input.c b/net/sctp/input.c
index 2e4a8646dbc3..693fd0804810 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -142,7 +142,8 @@ int sctp_rcv(struct sk_buff *skb)
         __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));
diff --git a/net/sctp/output.c b/net/sctp/output.c
index 47bfba6c03ec..2d65b7a7330b 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -531,7 +531,7 @@ int sctp_packet_transmit(struct sctp_packet *packet)
          * 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
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index b78e3be69013..cc0b592698f9 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -1411,4 +1411,6 @@ MODULE_ALIAS("net-pf-" __stringify(PF_INET) "-proto-132");
 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");