From f0668dc0d5125148ebfda47c9804127c928a2782 Mon Sep 17 00:00:00 2001
From: Johann Latocha
Date: Tue, 8 May 2012 19:54:30 +0200
Subject: [KERNEL] rtt measurement improved

---
 src/config.h       |  1 +
 src/kernel/dnbd3.h |  1 +
 src/kernel/net.c   | 19 ++++++++++++++++---
 3 files changed, 18 insertions(+), 3 deletions(-)

(limited to 'src')

diff --git a/src/config.h b/src/config.h
index 58ca9fc..b74ceab 100644
--- a/src/config.h
+++ b/src/config.h
@@ -31,6 +31,7 @@
 #define TIMER_INTERVAL_HEARTBEAT 10*HZ
 #define TIMER_INTERVAL_PANIC 1*HZ
 #define NUMBER_SERVERS 8
+#define RTT_THRESHOLD 1000
 
 // block device
 #define KERNEL_SECTOR_SIZE 512
diff --git a/src/kernel/dnbd3.h b/src/kernel/dnbd3.h
index 038cfb6..0e408dc 100644
--- a/src/kernel/dnbd3.h
+++ b/src/kernel/dnbd3.h
@@ -37,6 +37,7 @@ typedef struct
     char host[16];
     char port[6];
     uint64_t rtt;
+    uint64_t rtts[4];
     struct socket *sock;
     struct kobject kobj;
 } dnbd3_server_t;
diff --git a/src/kernel/net.c b/src/kernel/net.c
index 684ceb6..bc2f510 100644
--- a/src/kernel/net.c
+++ b/src/kernel/net.c
@@ -193,6 +193,8 @@ int dnbd3_net_discover(void *data)
     struct timeval start, end;
     uint64_t t1, t2, best_rtt = 0;
     int i, num = 0;
+    int turn = 0;
+    int ready = 0;
 
     struct timeval timeout;
     timeout.tv_sec = SOCKET_TIMEOUT_CLIENT_DISCOVERY;
@@ -308,9 +310,16 @@ int dnbd3_net_discover(void *data)
 
             t1 = (start.tv_sec*1000000ull) + start.tv_usec;
             t2 = (end.tv_sec*1000000ull) + end.tv_usec;
-            dev->alt_servers[i].rtt = t2 -t1;
+            dev->alt_servers[i].rtts[turn] = t2 -t1;
 
-            if ( best_rtt > dev->alt_servers[i].rtt )
+            dev->alt_servers[i].rtt = ( dev->alt_servers[i].rtts[0]
+                                       +dev->alt_servers[i].rtts[1]
+                                       +dev->alt_servers[i].rtts[2]
+                                       +dev->alt_servers[i].rtts[3] ) / 4;
+
+
+
+            if ( best_rtt > dev->alt_servers[i].rtt + RTT_THRESHOLD)
             {
             	best_rtt = dev->alt_servers[i].rtt;
             	strcpy(best_server, current_server);
@@ -330,7 +339,7 @@ int dnbd3_net_discover(void *data)
             continue;
 
         // take server with lowest rtt
-        if (num > 1 && strcmp(dev->cur_server.host, best_server) && !kthread_should_stop())
+        if (ready && num > 1 && strcmp(dev->cur_server.host, best_server) && !kthread_should_stop())
         {
             printk("INFO: Server %s on %s is faster (%lluus)\n", best_server, dev->disk->disk_name, best_rtt);
         	kfree(buf);
@@ -346,6 +355,10 @@ int dnbd3_net_discover(void *data)
             dev->cur_server.rtt = best_rtt;
         }
 
+        turn = (turn +1) % 4;
+        if (turn == 3)
+            ready = 1;
+
     }
     kfree(buf);
     return 0;
-- 
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