[ovs-dev] [PATCH V4 1/4] bfd: Implement BFD decay.

Alex Wang alexw at nicira.com
Thu Aug 15 21:29:52 UTC 2013


When there is no incoming data traffic at the interface for a period,
BFD decay allows the bfd session to increase the min_rx. This is
helpful in that some interfaces may be idle for long a time. And cpu
consumption can be reduced by processing fewer bfd control packets.

Signed-off-by: Alex Wang <alexw at nicira.com>

---

v3 -> v4:
- remove the change about "do not allow decay when decay_min_rx
  is less than rmt_min_tx" in v3.
- refine the decay algorithm.


v2 -> v3:
- refine the decay algorithm.
- add comments about the decay and decay algorithm.
- reset decay_detect_time when state goes to STATE_UP and
  decay_min_rx is configured..
- reset the bfd->min_rx to cfg_min_rx when state goes
  to STATE_DOWN and bfd is in decay.
- do not allow bfd to call bfd_may_decay when decay_min_rx
  is less than rmt_min_tx.
- reset the decay_detect_time when netdev is changed and
  decay_min_rx is configured.
- add two more unit tests.

v1 -> v2:
- add 'in_decay' boolean variable to bfd struct
  and simplify code.
- include unit test to this patch.

---
 lib/bfd.c              |  136 ++++++++++++++++++++++-
 lib/bfd.h              |    5 +-
 ofproto/ofproto-dpif.c |    7 +-
 tests/bfd.at           |  279 ++++++++++++++++++++++++++++++++++++++++++++++--
 vswitchd/vswitch.xml   |   10 ++
 5 files changed, 421 insertions(+), 16 deletions(-)

diff --git a/lib/bfd.c b/lib/bfd.c
index 74b27c4..89ba4a9 100644
--- a/lib/bfd.c
+++ b/lib/bfd.c
@@ -27,6 +27,7 @@
 #include "hash.h"
 #include "hmap.h"
 #include "list.h"
+#include "netdev.h"
 #include "netlink.h"
 #include "odp-util.h"
 #include "ofpbuf.h"
@@ -150,6 +151,9 @@ struct bfd {
     bool cpath_down;              /* Concatenated Path Down. */
     uint8_t mult;                 /* bfd.DetectMult. */
 
+    struct netdev *netdev;
+    uint64_t rx_packets;          /* Packets received by 'netdev'. */
+
     enum state state;             /* bfd.SessionState. */
     enum state rmt_state;         /* bfd.RemoteSessionState. */
 
@@ -185,6 +189,14 @@ struct bfd {
 
     atomic_bool check_tnl_key;    /* Verify tunnel key of inbound packets? */
     atomic_int ref_cnt;
+
+    /* BFD decay related variables. */
+    bool in_decay;                /* True when bfd is in decay. */
+    int decay_min_rx;             /* min_rx is set to decay_min_rx when */
+                                  /* in decay. */
+    int decay_rx_count;           /* Count rx packets received within decay */
+                                  /* detect interval. */
+    long long int decay_detect_time; /* Decay detection time. */
 };
 
 static struct ovs_mutex mutex = OVS_MUTEX_INITIALIZER;
@@ -207,6 +219,9 @@ static void bfd_set_state(struct bfd *, enum state, enum diag)
 static uint32_t generate_discriminator(void) OVS_REQUIRES(mutex);
 static void bfd_put_details(struct ds *, const struct bfd *)
     OVS_REQUIRES(mutex);
+static uint64_t bfd_rx_packets(const struct bfd *) OVS_REQUIRES(mutex);
+static void bfd_try_decay(struct bfd *) OVS_REQUIRES(mutex);
+static void bfd_decay_update(struct bfd *) OVS_REQUIRES(mutex);
 static void bfd_unixctl_show(struct unixctl_conn *, int argc,
                              const char *argv[], void *aux OVS_UNUSED);
 static void bfd_unixctl_set_forwarding_override(struct unixctl_conn *,
@@ -254,14 +269,16 @@ bfd_get_status(const struct bfd *bfd, struct smap *smap)
  * handle for the session, or NULL if BFD is not enabled according to 'cfg'.
  * Also returns NULL if cfg is NULL. */
 struct bfd *
-bfd_configure(struct bfd *bfd, const char *name, const struct smap *cfg)
-    OVS_EXCLUDED(mutex)
+bfd_configure(struct bfd *bfd, const char *name, const struct smap *cfg,
+              struct netdev *netdev) OVS_EXCLUDED(mutex)
 {
     static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
     static atomic_uint16_t udp_src = ATOMIC_VAR_INIT(0);
 
+    int decay_min_rx;
     long long int min_tx, min_rx;
     bool need_poll = false;
+    bool cfg_min_rx_changed = false;
     bool cpath_down;
     const char *hwaddr;
     uint8_t ea[ETH_ADDR_LEN];
@@ -292,6 +309,8 @@ bfd_configure(struct bfd *bfd, const char *name, const struct smap *cfg)
         bfd->min_tx = 1000;
         bfd->mult = 3;
         atomic_init(&bfd->ref_cnt, 1);
+        bfd->netdev = netdev_ref(netdev);
+        bfd->in_decay = false;
 
         /* RFC 5881 section 4
          * The source port MUST be in the range 49152 through 65535.  The same
@@ -327,6 +346,22 @@ bfd_configure(struct bfd *bfd, const char *name, const struct smap *cfg)
             || (!bfd_in_poll(bfd) && bfd->cfg_min_rx > bfd->min_rx)) {
             bfd->min_rx = bfd->cfg_min_rx;
         }
+        cfg_min_rx_changed = true;
+        need_poll = true;
+    }
+
+    decay_min_rx = smap_get_int(cfg, "decay_min_rx", 0);
+    if (bfd->decay_min_rx != decay_min_rx || cfg_min_rx_changed) {
+        if (decay_min_rx > 0 && decay_min_rx < bfd->cfg_min_rx) {
+            VLOG_WARN("%s: decay_min_rx cannot be less than %lld ms",
+                      bfd->name, bfd->cfg_min_rx);
+            bfd->decay_min_rx = 0;
+        } else {
+            bfd->decay_min_rx = decay_min_rx;
+        }
+        /* Resets decay. */
+        bfd->in_decay = false;
+        bfd_decay_update(bfd);
         need_poll = true;
     }
 
@@ -378,6 +413,7 @@ bfd_unref(struct bfd *bfd) OVS_EXCLUDED(mutex)
         if (orig == 1) {
             ovs_mutex_lock(&mutex);
             hmap_remove(all_bfds, &bfd->node);
+            netdev_close(bfd->netdev);
             free(bfd->name);
             free(bfd);
             ovs_mutex_unlock(&mutex);
@@ -403,12 +439,27 @@ bfd_wait(const struct bfd *bfd) OVS_EXCLUDED(mutex)
 void
 bfd_run(struct bfd *bfd) OVS_EXCLUDED(mutex)
 {
+    long long int now;
+    bool old_in_decay;
+
     ovs_mutex_lock(&mutex);
-    if (bfd->state > STATE_DOWN && time_msec() >= bfd->detect_time) {
+    now = time_msec();
+    old_in_decay = bfd->in_decay;
+
+    if (bfd->state > STATE_DOWN && now >= bfd->detect_time) {
         bfd_set_state(bfd, STATE_DOWN, DIAG_EXPIRED);
     }
 
-    if (bfd->min_tx != bfd->cfg_min_tx || bfd->min_rx != bfd->cfg_min_rx) {
+    /* Decay may only happen when state is STATE_UP, bfd->decay_min_rx is
+     * configured, and decay_detect_time is reached. */
+    if (bfd->state == STATE_UP && bfd->decay_min_rx > 0
+        && now >= bfd->decay_detect_time) {
+        bfd_try_decay(bfd);
+    }
+
+    if (bfd->min_tx != bfd->cfg_min_tx
+        || (bfd->min_rx != bfd->cfg_min_rx && bfd->min_rx != bfd->decay_min_rx)
+        || bfd->in_decay != old_in_decay) {
         bfd_poll(bfd);
     }
     ovs_mutex_unlock(&mutex);
@@ -536,6 +587,9 @@ bfd_process_packet(struct bfd *bfd, const struct flow *flow,
     /* This function is designed to follow section RFC 5880 6.8.6 closely. */
 
     ovs_mutex_lock(&mutex);
+    /* Increments the decay rx counter. */
+    bfd->decay_rx_count++;
+
     if (flow->nw_ttl != 255) {
         /* XXX Should drop in the kernel to prevent DOS. */
         goto out;
@@ -685,6 +739,23 @@ bfd_process_packet(struct bfd *bfd, const struct flow *flow,
 out:
     ovs_mutex_unlock(&mutex);
 }
+
+/* Must be called when the netdev owned by 'bfd' should change. */
+void
+bfd_set_netdev(struct bfd *bfd, const struct netdev *netdev)
+    OVS_EXCLUDED(mutex)
+{
+    ovs_mutex_lock(&mutex);
+    if (bfd->netdev != netdev) {
+        netdev_close(bfd->netdev);
+        bfd->netdev = netdev_ref(netdev);
+        if (bfd->decay_min_rx) {
+            bfd_decay_update(bfd);
+        }
+    }
+    ovs_mutex_unlock(&mutex);
+}
+
 
 static bool
 bfd_forwarding__(const struct bfd *bfd) OVS_REQUIRES(mutex)
@@ -712,7 +783,7 @@ bfd_poll(struct bfd *bfd) OVS_REQUIRES(mutex)
     if (bfd->state > STATE_DOWN && !bfd_in_poll(bfd)
         && !(bfd->flags & FLAG_FINAL)) {
         bfd->poll_min_tx = bfd->cfg_min_tx;
-        bfd->poll_min_rx = bfd->cfg_min_rx;
+        bfd->poll_min_rx = bfd->in_decay ? bfd->decay_min_rx : bfd->cfg_min_rx;
         bfd->flags |= FLAG_POLL;
         bfd->next_tx = 0;
         VLOG_INFO_RL(&rl, "%s: Initiating poll sequence", bfd->name);
@@ -885,10 +956,65 @@ bfd_set_state(struct bfd *bfd, enum state state, enum diag diag)
             bfd->rmt_flags = 0;
             bfd->rmt_disc = 0;
             bfd->rmt_min_tx = 0;
+            /* Resets the min_rx if in_decay. */
+            if (bfd->in_decay) {
+                bfd->min_rx = bfd->cfg_min_rx;
+                bfd->in_decay = false;
+            }
+        }
+        /* Resets the decay when state changes to STATE_UP
+         * and decay_min_rx is configured. */
+        if (bfd->state == STATE_UP && bfd->decay_min_rx) {
+            bfd_decay_update(bfd);
         }
     }
 }
 
+static uint64_t
+bfd_rx_packets(const struct bfd *bfd) OVS_REQUIRES(mutex)
+{
+    struct netdev_stats stats;
+
+    if (!netdev_get_stats(bfd->netdev, &stats)) {
+        return stats.rx_packets;
+    } else {
+        return 0;
+    }
+}
+
+/* Decays the bfd->min_rx to bfd->decay_min_rx when 'diff' is less than
+ * the 'expect' value.
+ *
+ * The 'diff' is the difference between current interface rx_packets stats
+ * and last-time check.  The 'expect' is the recorded number of bfd control
+ * packets received within an approximately decay_min_rx (2000 ms if
+ * decay_min_rx is less than 2000 ms) interval.
+ *
+ * Note, since the update of rx_packets stats at interface happens every
+ * 2000 ms and is asynchronous to the bfd_rx_packets() function, the
+ * 'diff' value can be jittered.  And the maximum jitter can be
+ * approximately (2000 ms / bfd->cfg_min_rx).  So, a value greater than this
+ * is added to 'expect' to compensate for the jitter. */
+static void
+bfd_try_decay(struct bfd *bfd) OVS_REQUIRES(mutex)
+{
+    int64_t diff, expect;
+
+    diff = bfd_rx_packets(bfd) - bfd->rx_packets;
+    expect = bfd->decay_rx_count + (2000 / bfd->cfg_min_rx + 10);
+    bfd->in_decay = diff <= expect ? true : false;
+    bfd_decay_update(bfd);
+}
+
+/* Updates the rx_packets, decay_rx_count and decay_detect_time. */
+static void
+bfd_decay_update(struct bfd * bfd) OVS_REQUIRES(mutex)
+{
+    bfd->rx_packets = bfd_rx_packets(bfd);
+    bfd->decay_rx_count = 0;
+    bfd->decay_detect_time = MAX(bfd->decay_min_rx, 2000) + time_msec();
+}
+
 static uint32_t
 generate_discriminator(void)
 {
diff --git a/lib/bfd.h b/lib/bfd.h
index 67d012e..0e1e33d 100644
--- a/lib/bfd.h
+++ b/lib/bfd.h
@@ -24,6 +24,7 @@
 struct bfd;
 struct flow;
 struct flow_wildcards;
+struct netdev;
 struct ofpbuf;
 struct smap;
 
@@ -40,11 +41,13 @@ void bfd_process_packet(struct bfd *, const struct flow *,
                         const struct ofpbuf *);
 
 struct bfd *bfd_configure(struct bfd *, const char *name,
-                          const struct smap *smap);
+                          const struct smap *smap,
+                          struct netdev *netdev);
 struct bfd *bfd_ref(const struct bfd *);
 void bfd_unref(struct bfd *);
 
 bool bfd_forwarding(const struct bfd *);
 void bfd_get_status(const struct bfd *, struct smap *);
+void bfd_set_netdev(struct bfd *, const struct netdev *);
 
 #endif /* bfd.h */
diff --git a/ofproto/ofproto-dpif.c b/ofproto/ofproto-dpif.c
index 229b16c..a52ec1b 100644
--- a/ofproto/ofproto-dpif.c
+++ b/ofproto/ofproto-dpif.c
@@ -1891,6 +1891,10 @@ port_modified(struct ofport *port_)
         cfm_set_netdev(port->cfm, port->up.netdev);
     }
 
+    if (port->bfd) {
+        bfd_set_netdev(port->bfd, port->up.netdev);
+    }
+
     if (port->is_tunnel && tnl_port_reconfigure(port, port->up.netdev,
                                                 port->odp_port)) {
         ofproto_dpif_cast(port->up.ofproto)->backer->need_revalidate =
@@ -2025,7 +2029,8 @@ set_bfd(struct ofport *ofport_, const struct smap *cfg)
     struct bfd *old;
 
     old = ofport->bfd;
-    ofport->bfd = bfd_configure(old, netdev_get_name(ofport->up.netdev), cfg);
+    ofport->bfd = bfd_configure(old, netdev_get_name(ofport->up.netdev),
+                                cfg, ofport->up.netdev);
     if (ofport->bfd != old) {
         ofproto->backer->need_revalidate = REV_RECONFIGURE;
     }
diff --git a/tests/bfd.at b/tests/bfd.at
index fb8b1d3..da45b27 100644
--- a/tests/bfd.at
+++ b/tests/bfd.at
@@ -20,9 +20,9 @@ AT_CHECK([ovs-appctl bfd/show $1 | sed -e '/Time:/d' | sed -e '/Discriminator/d'
 m4_define([BFD_CHECK_TX], [
 AT_CHECK([ovs-appctl bfd/show $1 | sed -n '/TX Interval/p'],[0],
 [dnl
-	TX Interval: Approx 1000ms
-	Local Minimum TX Interval: $2
-	Remote Minimum TX Interval: $3
+	TX Interval: Approx $2
+	Local Minimum TX Interval: $3
+	Remote Minimum TX Interval: $4
 ])
 ])
 
@@ -30,8 +30,8 @@ m4_define([BFD_CHECK_RX], [
 AT_CHECK([ovs-appctl bfd/show $1 | sed -n '/RX Interval/p'],[0],
 [dnl
 	RX Interval: Approx $2
-	Local Minimum RX Interval: $2
-	Remote Minimum RX Interval: $3
+	Local Minimum RX Interval: $3
+	Remote Minimum RX Interval: $4
 ])
 ])
 AT_SETUP([bfd - basic config on different bridges])
@@ -202,14 +202,14 @@ BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [N
 #Edit the min Tx value.
 AT_CHECK([ovs-vsctl set interface p0 bfd:min_tx=200])
 for i in `seq 0 20`; do ovs-appctl time/warp 100; done
-BFD_CHECK_TX([p0], [200ms], [100ms])
-BFD_CHECK_TX([p1], [100ms], [200ms])
+BFD_CHECK_TX([p0], [1000ms], [200ms], [100ms])
+BFD_CHECK_TX([p1], [1000ms], [100ms], [200ms])
 
 #Edit the min Rx value.
 AT_CHECK([ovs-vsctl set interface p1 bfd:min_rx=300])
 for i in `seq 0 20`; do ovs-appctl time/warp 100; done
-BFD_CHECK_RX([p1], [300ms], [1000ms])
-BFD_CHECK_RX([p0], [1000ms], [300ms])
+BFD_CHECK_RX([p1], [300ms], [300ms], [1000ms])
+BFD_CHECK_RX([p0], [1000ms], [1000ms], [300ms])
 
 OVS_VSWITCHD_STOP
 AT_CLEANUP
@@ -247,3 +247,264 @@ This flow is handled by the userspace slow path because it:
 
 OVS_VSWITCHD_STOP
 AT_CLEANUP
+
+# Tests below are for bfd decay features.
+AT_SETUP([bfd - bfd decay])
+OVS_VSWITCHD_START([add-br br1 -- set bridge br1 datapath-type=dummy -- \
+                    add-port br1 p1 -- set Interface p1 type=patch \
+                    options:peer=p0 ofport_request=2 -- \
+                    add-port br0 p0 -- set Interface p0 type=patch \
+                    options:peer=p1 ofport_request=1 -- \
+                    set Interface p0 bfd:enable=true bfd:min_tx=300 bfd:min_rx=300 bfd:decay_min_rx=3000 -- \
+                    set Interface p1 bfd:enable=true bfd:min_tx=500 bfd:min_rx=500])
+
+ovs-appctl time/stop
+
+# wait for local session state to go from down to up.
+for i in `seq 0 2`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [init], [No Diagnostic])
+
+
+# Test-1 BFD decay: decay to decay_min_rx
+# bfd:decay_min_rx is set to 3000ms after the local state of p0 goes up,
+# so for the first 2500ms, there should be no change.
+for i in `seq 0 3`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+
+# advance the clock by 500ms.
+ovs-appctl time/warp 500
+# now at 3000ms, min_rx should decay to 3000ms and there should be
+# poll sequence flags.
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [3000ms], [3000ms], [500ms])
+
+# since the tx_min of p0 is still 500ms, after 500ms from decay,
+# the control message will be sent from p0 to p1, and p1 'flag'
+# will go back to none.
+ovs-appctl time/warp 500
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+
+# the rx_min of p0 is 3000ms now, and p1 will send next control message
+# 3000ms after decay. so, advance clock by 2500ms to make that happen.
+for i in `seq 0 4`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [3000ms], [3000ms], [500ms])
+# End of Test-1 ###############################################################
+
+
+# Test-2 BFD decay: go back to cfg_min_rx when there is traffic
+# receive packet at 1/100ms rate for 3000ms.
+for i in `seq 0 30`
+do
+    ovs-appctl time/warp 100
+    AT_CHECK([ovs-ofctl packet-out br1 3 2  "90e2ba01475000101856b2e80806000108000604000100101856b2e80202020300000000000002020202"],
+             [0], [stdout], [])
+done
+# after a decay interval (3000ms), the p0 min_rx will go back to
+# cfg_min_rx. there should be poll sequence flags.
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+
+# 500ms later, both direction will send control messages,
+# and their 'flag' will go back to none.
+ovs-appctl time/warp 500
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+# End of Test-2 ###############################################################
+
+
+# Test-3 BFD decay: go back to cfg_min_rx when decay_min_rx is changed
+# advance the clock by 2500ms to 3000m after restore of
+# min_rx. p0 is decayed, and there should be the poll sequence flags.
+for i in `seq 0 4`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [3000ms], [3000ms], [500ms])
+
+# advance the clock, to make 'flag' go back to none.
+for i in `seq 0 5`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+
+# change decay_min_rx to 1000ms.
+# for decay_min_rx < 2000ms, the decay detection time is set to 2000ms.
+# this should firstly reset the min_rx and start poll sequence.
+AT_CHECK([ovs-vsctl set Interface p0 bfd:decay_min_rx=1000])
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+
+# for the following 1500ms, there should be no decay,
+# since the decay_detect_time is set to 2000ms.
+for i in `seq 0 2`
+do
+    ovs-appctl time/warp 500
+    BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+    BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+done
+
+ovs-appctl time/warp 500
+# at 2000ms, decay should happen and there should be the poll sequence flags.
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [1000ms], [1000ms], [500ms])
+# advance the clock, so 'flag' go back to none.
+for i in `seq 0 4`; do ovs-appctl time/warp 500; done
+# End of Test-3 ###############################################################
+
+
+# Test-4 BFD decay: set min_rx to 800ms.
+# this should firstly reset the min_rx and then re-decay to 1000ms.
+AT_CHECK([ovs-vsctl set Interface p0 bfd:min_rx=800])
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [800ms], [800ms], [500ms])
+
+# for the following 1600ms, there should be no decay,
+# since the decay detection time is set to 2000ms.
+for i in `seq 0 1`
+do
+    ovs-appctl time/warp 800
+    BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+    BFD_CHECK_RX([p0], [800ms], [800ms], [500ms])
+done
+
+ovs-appctl time/warp 400
+# at 2000ms, decay should happen and there should be the poll sequence flags.
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [1000ms], [1000ms], [500ms])
+# advance the clock, so 'flag' go back to none.
+for i in `seq 0 4`; do ovs-appctl time/warp 500; done
+# End of Test-4 ###############################################################
+
+
+# Test-5 BFD decay: set min_rx to 300ms and decay_min_rx to 5000ms together.
+AT_CHECK([ovs-vsctl set Interface p0 bfd:min_rx=300 bfd:decay_min_rx=5000])
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+
+# for decay_min_rx > 2000ms, the decay detection time is set to
+# decay_min_rx (5000ms).
+# for the following 4500ms, there should be no decay,
+# since the decay detection time is set to 5000ms.
+for i in `seq 0 8`
+do
+    ovs-appctl time/warp 500
+    BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+    BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+done
+
+ovs-appctl time/warp 500
+# at 5000ms, decay should happen and there should be the poll sequence flags.
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [5000ms], [5000ms], [500ms])
+# advance the clock, to make 'flag' go back to none.
+for i in `seq 0 9`; do ovs-appctl time/warp 500; done
+# End of Test-5 ###############################################################
+
+
+# Test-6 BFD decay: set decay_min_rx to 0 to disable bfd decay.
+AT_CHECK([ovs-vsctl set Interface p0 bfd:decay_min_rx=0])
+# min_rx is reset, and there should be the poll sequence flags.
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+for i in `seq 0 20`
+do
+    ovs-appctl time/warp 500
+    BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+    BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+done
+# End of Test-6 ################################################################
+
+
+# Test-7 BFD decay: rmt_min_tx is greater than decay_min_rx
+AT_CHECK([ovs-vsctl set Interface p0 bfd:decay_min_rx=3000 -- set interface p1 bfd:min_tx=5000])
+# there will be poll sequences from both sides. and it is hard to determine the
+# order. so just skip 10000ms and check the RX/TX. at that time, p0 should be in decay already.
+for i in `seq 0 19`; do echo $i; ovs-appctl bfd/show; ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [5000ms])
+BFD_CHECK_RX([p0], [5000ms], [3000ms], [500ms])
+# then, there should be no change of status,
+for i in `seq 0 9`
+do
+    ovs-appctl time/warp 500
+    BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+    BFD_CHECK_TX([p0], [500ms], [300ms], [5000ms])
+    BFD_CHECK_RX([p0], [5000ms], [3000ms], [500ms])
+done
+# reset the p1's min_tx to 500ms.
+AT_CHECK([ovs-vsctl set Interface p1 bfd:min_tx=500])
+# check the poll sequence. since p0 has been in decay, now the RX will show 3000ms.
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [final], [up], [No Diagnostic])
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [3000ms], [3000ms], [500ms])
+# advance the clock by 3000ms, at that time, p1 will send the control packets.
+# then there will be no poll flags.
+for i in `seq 0 5`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [none], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [3000ms], [3000ms], [500ms])
+# End of Test-7 ###############################################################
+
+
+# Test-8 BFD decay: state up->down->up.
+# turn bfd off on p1
+AT_CHECK([ovs-vsctl set Interface p1 bfd:enable=false])
+
+# check the state change of bfd on p0. After 9000 ms (3 min_rx intervals)
+for i in `seq 0 8`; do ovs-appctl time/warp 1000; done
+BFD_CHECK([p0], [false], [false], [none], [down], [Control Detection Time Expired], [none], [down], [No Diagnostic])
+BFD_CHECK_TX([p0], [1000ms], [1000ms], [0ms])
+BFD_CHECK_RX([p0], [300ms], [300ms], [1ms])
+
+# resume the bfd on p1. the bfd should not go to decay mode direclty.
+AT_CHECK([ovs-vsctl set Interface p1 bfd:enable=true])
+for i in `seq 0 1`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [Control Detection Time Expired], [none], [up], [No Diagnostic])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [500ms], [300ms], [500ms])
+
+# since the decay_min_rx is still 3000ms, so after 3000ms, there should be the decay and poll sequence.
+for i in `seq 0 5`; do ovs-appctl time/warp 500; done
+BFD_CHECK([p0], [true], [false], [none], [up], [Control Detection Time Expired], [final], [up], [No Diagnostic])
+BFD_CHECK([p1], [true], [false], [none], [up], [No Diagnostic], [poll], [up], [Control Detection Time Expired])
+BFD_CHECK_TX([p0], [500ms], [300ms], [500ms])
+BFD_CHECK_RX([p0], [3000ms], [3000ms], [500ms])
+# End of Test-8 ################################################################
+
+OVS_VSWITCHD_STOP
+AT_CLEANUP
\ No newline at end of file
diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index b89d58c..b73a612 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -1880,6 +1880,16 @@
           specified.  Defaults to <code>100</code>.
       </column>
 
+      <column name="bfd" key="decay_min_rx" type='{"type": "integer"}'>
+          <code>decay_min_rx</code> is used to set the <code>min_rx</code>,
+          when there is no obvious incoming data traffic at the interface.
+          It cannot be less than the <code>min_rx</code>. The decay feature
+          is disable by setting the <code>decay_min_rx</code> to 0. And the
+          feature is reset everytime itself or <code>min_rx</code> is
+          reconfigured.
+      </column>
+
+
       <column name="bfd" key="cpath_down" type='{"type": "boolean"}'>
           Concatenated path down may be used when the local system should not
           have traffic forwarded to it for some reason other than a connectivty
-- 
1.7.9.5




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