From d6dd113a968a2cc089599dec99f201423e52f460 Mon Sep 17 00:00:00 2001
From: Jerry <isjerryxiao@outlook.com>
Date: Wed, 7 Dec 2022 13:02:20 +0800
Subject: [PATCH] test median smoothing

---
 doc/bird.sgml        | 10 +++++-----
 proto/babel/babel.c  | 43 ++++++++++++++++++++++++++++++++++++++-----
 proto/babel/babel.h  |  8 ++++++--
 proto/babel/config.Y |  6 +++---
 4 files changed, 52 insertions(+), 15 deletions(-)

diff --git a/doc/bird.sgml b/doc/bird.sgml
index 430ebad8..695116d6 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -1898,7 +1898,7 @@ protocol babel [<name>] {
 		rtt cost <number>;
 		rtt min <time>;
 		rtt max <time>;
-		rtt decay <number>;
+		rtt winlen <number>;
 		send timestamps <switch>;
 		authentication none|mac [permissive];
 		password "&lt;text&gt;";
@@ -2037,10 +2037,10 @@ protocol babel [<name>] {
       The maximum RTT above which the full RTT cost will start be applied.
       Default: 120 ms
 
-      <tag><label id="babel-rtt-decay">rtt decay <m/number/</tag>
-      The decay factor used for the exponentional moving average of the RTT
-      samples from each neighbour, in units of 1/256. Higher values discards old
-      RTT samples faster. Must be between 1 and 256. Default: 42
+      <tag><label id="babel-rtt-winlen">rtt winlen <m/number/</tag>
+      The window length user to calculate median of the RTT
+      samples from each neighbour, Lower values discards old
+      RTT samples faster. Must be between 1 and 65535. Default: 100
 
       <tag><label id="babel-send-timestamps">send timestamps <m/switch/</tag>
       Whether to send the timestamps used for RTT calculation on this interface.
diff --git a/proto/babel/babel.c b/proto/babel/babel.c
index 91f97053..62eb9fe7 100644
--- a/proto/babel/babel.c
+++ b/proto/babel/babel.c
@@ -536,6 +536,10 @@ babel_get_neighbor(struct babel_iface *ifa, ip_addr addr)
   init_list(&nbr->requests);
   add_tail(&ifa->neigh_list, NODE nbr);
 
+  nbr->srtt_pool = mb_allocz(ifa->pool, ifa->cf->rtt_win_len*sizeof(btime));
+  nbr->srtt_pool_sorted = mb_allocz(ifa->pool, ifa->cf->rtt_win_len*sizeof(btime));
+  nbr->srtt_poll_idx = nbr->srtt_pool_len = 0;
+
   return nbr;
 }
 
@@ -560,6 +564,8 @@ babel_flush_neighbor(struct babel_proto *p, struct babel_neighbor *nbr)
 
   nbr->ifa = NULL;
   rem_node(NODE nbr);
+  mb_free(nbr->srtt_pool);
+  mb_free(nbr->srtt_pool_sorted);
   mb_free(nbr);
 }
 
@@ -1304,6 +1310,21 @@ babel_handle_hello(union babel_msg *m, struct babel_iface *ifa)
   }
 }
 
+static int
+babel_btime_cmp(const void *b1, const void *b2)
+{
+  btime r;
+  switch (r = *(btime*)b1 - *(btime*)b2)
+  {
+  case 0:
+    return 0;
+    break;
+  default:
+    return r > (btime)0 ? 1 : -1;
+    break;
+  }
+}
+
 void
 babel_handle_ihu(union babel_msg *m, struct babel_iface *ifa)
 {
@@ -1341,12 +1362,24 @@ babel_handle_ihu(union babel_msg *m, struct babel_iface *ifa)
 
     if (n->srtt)
     {
-      uint decay = n->ifa->cf->rtt_decay;
-
-      n->srtt = (decay * rtt_sample + (256 - decay) * n->srtt) / 256;
+      u16 pool_idx = n->srtt_poll_idx % n->ifa->cf->rtt_win_len;
+      n->srtt_poll_idx = pool_idx + 1;
+      *(n->srtt_pool + pool_idx) = rtt_sample;
+      if (n->srtt_pool_len < n->ifa->cf->rtt_win_len)
+        n->srtt_pool_len++;
+      memcpy(n->srtt_pool_sorted, n->srtt_pool, (size_t)n->srtt_pool_len*sizeof(btime));
+      // use qsort for now for testing
+      qsort(n->srtt_pool_sorted, (size_t)n->srtt_pool_len, sizeof(btime), babel_btime_cmp);
+      int mid = n->srtt_pool_len / (u16)2;
+      if (!n->srtt_pool_len || n->srtt_pool_len % (u16)2)
+        n->srtt = *(n->srtt_pool_sorted + mid);
+      else
+        n->srtt = (*(n->srtt_pool_sorted + mid - (u16)1) + *(n->srtt_pool_sorted + mid)) / (u16)2;
+    }
+    else {
+      *(n->srtt_pool) = n->srtt = rtt_sample;
+      n->srtt_poll_idx = n->srtt_pool_len = 1;
     }
-    else
-      n->srtt = rtt_sample;
 
     TRACE(D_EVENTS, "RTT sample for neighbour %I on %s: %u us (srtt %u.%03u ms)",
           n->addr, ifa->ifname, rtt_sample, n->srtt/1000, n->srtt%1000);
diff --git a/proto/babel/babel.h b/proto/babel/babel.h
index d4439fde..955c40d3 100644
--- a/proto/babel/babel.h
+++ b/proto/babel/babel.h
@@ -58,7 +58,7 @@
 #define BABEL_RTT_MAX_VALUE		(600 S_)
 #define BABEL_RTT_MIN			(10 MS_)
 #define BABEL_RTT_MAX			(120 MS_)
-#define BABEL_RTT_DECAY			42
+#define BABEL_RTT_WINLEN			100
 
 /*
  * Constants for calculating metric smoothing. Chosen so that:
@@ -163,7 +163,7 @@ struct babel_iface_config {
   btime rtt_min;			/* rtt above which to start penalising metric */
   btime rtt_max;			/* max rtt metric penalty applied above this */
   u16 rtt_cost;			/* metric penalty to apply at rtt_max */
-  u16 rtt_decay;			/* decay of neighbour RTT (units of 1/256) */
+  u16 rtt_win_len;			/* smoothing windows length */
   u8  rtt_send;			/* whether to send timestamps on this interface */
 
   u16 rx_buffer;			/* RX buffer size, 0 for MTU */
@@ -256,6 +256,10 @@ struct babel_neighbor {
   u32 last_tstamp;
   btime last_tstamp_rcvd;
   btime srtt;
+  btime *srtt_pool;  // an array of btime
+  btime *srtt_pool_sorted;
+  u16 srtt_pool_len; // initial length
+  u16 srtt_poll_idx; // head
 
   u32 auth_pc;
   u8 auth_passed;
diff --git a/proto/babel/config.Y b/proto/babel/config.Y
index 55fb6108..6a14c993 100644
--- a/proto/babel/config.Y
+++ b/proto/babel/config.Y
@@ -26,7 +26,7 @@ CF_KEYWORDS(BABEL, INTERFACE, METRIC, RXCOST, HELLO, UPDATE, INTERVAL, PORT,
 	TYPE, WIRED, WIRELESS, TUNNEL, RX, TX, BUFFER, PRIORITY, LENGTH, CHECK,
         LINK, NEXT, HOP, IPV4, IPV6, BABEL_METRIC, SHOW, INTERFACES, NEIGHBORS,
 	ENTRIES, RANDOMIZE, ROUTER, ID, AUTHENTICATION, NONE, MAC, PERMISSIVE,
-        RTT, MIN, MAX, DECAY, SEND, TIMESTAMPS)
+        RTT, MIN, MAX, DECAY, WINLEN, SEND, TIMESTAMPS)
 
 CF_GRAMMAR
 
@@ -77,7 +77,7 @@ babel_iface_start:
   BABEL_IFACE->tx_priority = sk_priority_control;
   BABEL_IFACE->rtt_min = BABEL_RTT_MIN;
   BABEL_IFACE->rtt_max = BABEL_RTT_MAX;
-  BABEL_IFACE->rtt_decay = BABEL_RTT_DECAY;
+  BABEL_IFACE->rtt_win_len = BABEL_RTT_WINLEN;
   BABEL_IFACE->rtt_send = 1;
   BABEL_IFACE->check_link = 1;
 };
@@ -171,7 +171,7 @@ babel_iface_item:
  | RTT MIN expr_us { BABEL_IFACE->rtt_min = $3; }
  | RTT MAX expr_us { BABEL_IFACE->rtt_max = $3; }
  | RTT COST expr { BABEL_IFACE->rtt_cost = $3; if ($3 >= BABEL_INFINITY) cf_error("RTT cost must be < 65535"); }
- | RTT DECAY expr { BABEL_IFACE->rtt_decay = $3; if (($3 < 1) || ($3 > 256)) cf_error("RTT decay must be between 1-256"); }
+ | RTT WINLEN expr { BABEL_IFACE->rtt_win_len = $3; if (($3 < 1) || ($3 > 65535)) cf_error("RTT winlen must be between 1-65535"); }
  | SEND TIMESTAMPS bool { BABEL_IFACE->rtt_send = $3; }
  | password_list
  ;