diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
index 68577ef250..40e41e793e 100644
--- a/migration/dirtyrate.c
+++ b/migration/dirtyrate.c
@@ -83,14 +83,14 @@ static struct DirtyRateInfo *query_dirty_rate_info(void)
     return info;
 }
 
-static void reset_dirtyrate_stat(void)
+static void init_dirtyrate_stat(int64_t start_time, int64_t calc_time)
 {
     DirtyStat.total_dirty_samples = 0;
     DirtyStat.total_sample_count = 0;
     DirtyStat.total_block_mem_MB = 0;
     DirtyStat.dirty_rate = -1;
-    DirtyStat.start_time = 0;
-    DirtyStat.calc_time = 0;
+    DirtyStat.start_time = start_time;
+    DirtyStat.calc_time = calc_time;
 }
 
 static void update_dirtyrate_stat(struct RamblockDirtyInfo *info)
@@ -335,7 +335,6 @@ static void calculate_dirtyrate(struct DirtyRateConfig config)
     int64_t initial_time;
 
     rcu_register_thread();
-    reset_dirtyrate_stat();
     rcu_read_lock();
     initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
     if (!record_ramblock_hash_info(&block_dinfo, config, &block_count)) {
@@ -365,6 +364,8 @@ void *get_dirtyrate_thread(void *arg)
 {
     struct DirtyRateConfig config = *(struct DirtyRateConfig *)arg;
     int ret;
+    int64_t start_time;
+    int64_t calc_time;
 
     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_UNSTARTED,
                               DIRTY_RATE_STATUS_MEASURING);
@@ -373,6 +374,10 @@ void *get_dirtyrate_thread(void *arg)
         return NULL;
     }
 
+    start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
+    calc_time = config.sample_period_seconds;
+    init_dirtyrate_stat(start_time, calc_time);
+
     calculate_dirtyrate(config);
 
     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_MEASURING,