sctp: Update SWS avaoidance receiver side algorithm

We currently send window update SACKs every time we free up 1 PMTU
worth of data.  That a lot more SACKs then necessary.  Instead, we'll
now send back the actuall window every time we send a sack, and do
window-update SACKs when a fraction of the receive buffer has been
opened.  The fraction is controlled with a sysctl.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>

2 files changed, 10 insertions, 0 deletions

diff --git a/include/net/sctp/constants.h b/include/net/sctp/constants.h
index 58f714a3b670..63908840eef0 100644
--- a/include/net/sctp/constants.h
+++ b/include/net/sctp/constants.h
@@ -308,6 +308,10 @@ enum { SCTP_MAX_GABS = 16 };
 
 #define SCTP_DEFAULT_MINWINDOW  1500    /* default minimum rwnd size */
 #define SCTP_DEFAULT_MAXWINDOW  65535   /* default rwnd size */
+#define SCTP_DEFAULT_RWND_SHIFT  4      /* by default, update on 1/16 of
+                                         * rcvbuf, which is 1/8 of initial
+                                         * window
+                                         */
 #define SCTP_DEFAULT_MAXSEGMENT 1500    /* MTU size, this is the limit
                                          * to which we will raise the P-MTU.
                                          */
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index cd2e18778f81..90876b657775 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -231,6 +231,11 @@ extern struct sctp_globals {
         /* Flag to indicate whether computing and verifying checksum
          * is disabled. */
         int checksum_disable;
+
+        /* Threshold for rwnd update SACKS.  Receive buffer shifted this many
+         * bits is an indicator of when to send and window update SACK.
+         */
+        int rwnd_update_shift;
 } sctp_globals;
 
 #define sctp_rto_initial                (sctp_globals.rto_initial)
@@ -267,6 +272,7 @@ extern struct sctp_globals {
 #define sctp_prsctp_enable              (sctp_globals.prsctp_enable)
 #define sctp_auth_enable                (sctp_globals.auth_enable)
 #define sctp_checksum_disable           (sctp_globals.checksum_disable)
+#define sctp_rwnd_upd_shift             (sctp_globals.rwnd_update_shift)
 
 /* SCTP Socket type: UDP or TCP style. */
 typedef enum {