NFSv4.1: Try to eliminate outliers when updating target_highest_slotid

Look for sudden changes in the first and second derivatives in order
to eliminate outlier changes to target_highest_slotid (which are
due to out-of-order RPC replies).

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 60 insertions, 5 deletions

diff --git a/fs/nfs/nfs4session.c b/fs/nfs/nfs4session.c
index 066cfa101b41..ed5aa9fa9c7b 100644
--- a/fs/nfs/nfs4session.c
+++ b/fs/nfs/nfs4session.c
@@ -178,6 +178,8 @@ static void nfs4_reset_slot_table(struct nfs4_slot_table *tbl,
         tbl->highest_used_slotid = NFS4_NO_SLOT;
         tbl->target_highest_slotid = server_highest_slotid;
         tbl->server_highest_slotid = server_highest_slotid;
+        tbl->d_target_highest_slotid = 0;
+        tbl->d2_target_highest_slotid = 0;
         tbl->max_slotid = server_highest_slotid;
 }
 
@@ -292,6 +294,8 @@ void nfs41_set_target_slotid(struct nfs4_slot_table *tbl,
 {
         spin_lock(&tbl->slot_tbl_lock);
         nfs41_set_target_slotid_locked(tbl, target_highest_slotid);
+        tbl->d_target_highest_slotid = 0;
+        tbl->d2_target_highest_slotid = 0;
         spin_unlock(&tbl->slot_tbl_lock);
 }
 
@@ -307,16 +311,65 @@ static void nfs41_set_server_slotid_locked(struct nfs4_slot_table *tbl,
         tbl->server_highest_slotid = highest_slotid;
 }
 
+static s32 nfs41_derivative_target_slotid(s32 s1, s32 s2)
+{
+        s1 -= s2;
+        if (s1 == 0)
+                return 0;
+        if (s1 < 0)
+                return (s1 - 1) >> 1;
+        return (s1 + 1) >> 1;
+}
+
+static int nfs41_sign_s32(s32 s1)
+{
+        if (s1 > 0)
+                return 1;
+        if (s1 < 0)
+                return -1;
+        return 0;
+}
+
+static bool nfs41_same_sign_or_zero_s32(s32 s1, s32 s2)
+{
+        if (!s1 || !s2)
+                return true;
+        return nfs41_sign_s32(s1) == nfs41_sign_s32(s2);
+}
+
+/* Try to eliminate outliers by checking for sharp changes in the
+ * derivatives and second derivatives
+ */
+static bool nfs41_is_outlier_target_slotid(struct nfs4_slot_table *tbl,
+                u32 new_target)
+{
+        s32 d_target, d2_target;
+        bool ret = true;
+
+        d_target = nfs41_derivative_target_slotid(new_target,
+                        tbl->target_highest_slotid);
+        d2_target = nfs41_derivative_target_slotid(d_target,
+                        tbl->d_target_highest_slotid);
+        /* Is first derivative same sign? */
+        if (nfs41_same_sign_or_zero_s32(d_target, tbl->d_target_highest_slotid))
+                ret = false;
+        /* Is second derivative same sign? */
+        if (nfs41_same_sign_or_zero_s32(d2_target, tbl->d2_target_highest_slotid))
+                ret = false;
+        tbl->d_target_highest_slotid = d_target;
+        tbl->d2_target_highest_slotid = d2_target;
+        return ret;
+}
+
 void nfs41_update_target_slotid(struct nfs4_slot_table *tbl,
                 struct nfs4_slot *slot,
                 struct nfs4_sequence_res *res)
 {
         spin_lock(&tbl->slot_tbl_lock);
-        if (tbl->generation != slot->generation)
-                goto out;
-        nfs41_set_server_slotid_locked(tbl, res->sr_highest_slotid);
-        nfs41_set_target_slotid_locked(tbl, res->sr_target_highest_slotid);
-out:
+        if (!nfs41_is_outlier_target_slotid(tbl, res->sr_target_highest_slotid))
+                nfs41_set_target_slotid_locked(tbl, res->sr_target_highest_slotid);
+        if (tbl->generation == slot->generation)
+                nfs41_set_server_slotid_locked(tbl, res->sr_highest_slotid);
         spin_unlock(&tbl->slot_tbl_lock);
 }
 
diff --git a/fs/nfs/nfs4session.h b/fs/nfs/nfs4session.h
index 7db739370164..04f834cab16c 100644
--- a/fs/nfs/nfs4session.h
+++ b/fs/nfs/nfs4session.h
@@ -38,6 +38,8 @@ struct nfs4_slot_table {
                                                  * op for dynamic resizing */
         u32             target_highest_slotid;  /* Server max_slot target */
         u32             server_highest_slotid;  /* Server highest slotid */
+        s32             d_target_highest_slotid; /* Derivative */
+        s32             d2_target_highest_slotid; /* 2nd derivative */
         unsigned long   generation;             /* Generation counter for
                                                    target_highest_slotid */
         struct completion complete;