[PATCH] IPoIB: fix static rate calculation

Correct and simplify calculation of static rate.  We need to round up the
quotient of (local_rate - path_rate) / path_rate.  To round up we add
(path_rate - 1) to the numerator, so the quotient simplifies to (local_rate -
1) / path_rate.

No idea how I came up with the old formula.

Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 6 insertions, 8 deletions

diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
index 5a3b5c6a44..8d35475a1d 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
@@ -302,11 +302,10 @@ static void path_rec_completion(int status,
                         .sl            = pathrec->sl,
                         .port_num      = priv->port
                 };
+                int path_rate = ib_sa_rate_enum_to_int(pathrec->rate);
 
-                if (ib_sa_rate_enum_to_int(pathrec->rate) > 0)
-                        av.static_rate = (2 * priv->local_rate -
-                                          ib_sa_rate_enum_to_int(pathrec->rate) - 1) /
-                                (priv->local_rate ? priv->local_rate : 1);
+                if (path_rate > 0 && priv->local_rate > path_rate)
+                        av.static_rate = (priv->local_rate - 1) / path_rate;
 
                 ipoib_dbg(priv, "static_rate %d for local port %dX, path %dX\n",
                           av.static_rate, priv->local_rate,
diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
index f46932dc81..70208c3d21 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
@@ -258,13 +258,12 @@ static int ipoib_mcast_join_finish(struct ipoib_mcast *mcast,
                                 .traffic_class = mcast->mcmember.traffic_class
                         }
                 };
+                int path_rate = ib_sa_rate_enum_to_int(mcast->mcmember.rate);
 
                 av.grh.dgid = mcast->mcmember.mgid;
 
-                if (ib_sa_rate_enum_to_int(mcast->mcmember.rate) > 0)
-                        av.static_rate = (2 * priv->local_rate -
-                                          ib_sa_rate_enum_to_int(mcast->mcmember.rate) - 1) /
-                                (priv->local_rate ? priv->local_rate : 1);
+                if (path_rate > 0 && priv->local_rate > path_rate)
+                        av.static_rate = (priv->local_rate - 1) / path_rate;
 
                 ipoib_dbg_mcast(priv, "static_rate %d for local port %dX, mcmember %dX\n",
                                 av.static_rate, priv->local_rate,