migration/dirtyrate: Implement set_sample_page_period() and is_sample_period_valid()

Implement is_sample_period_valid() to check if the sample period is vaild and
do set_sample_page_period() to sleep specific time between sample actions.

Signed-off-by: Chuan Zheng <zhengchuan@huawei.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: David Edmondson <david.edmondson@oracle.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Message-Id: <1600237327-33618-10-git-send-email-zhengchuan@huawei.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/dirtyrate.c

@@ -27,6 +27,30 @@
 static int CalculatingState = DIRTY_RATE_STATUS_UNSTARTED;
 static struct DirtyRateStat DirtyStat;
 
+static int64_t set_sample_page_period(int64_t msec, int64_t initial_time)
+{
+    int64_t current_time;
+
+    current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    if ((current_time - initial_time) >= msec) {
+        msec = current_time - initial_time;
+    } else {
+        g_usleep((msec + initial_time - current_time) * 1000);
+    }
+
+    return msec;
+}
+
+static bool is_sample_period_valid(int64_t sec)
+{
+    if (sec < MIN_FETCH_DIRTYRATE_TIME_SEC ||
+        sec > MAX_FETCH_DIRTYRATE_TIME_SEC) {
+        return false;
+    }
+
+    return true;
+}
+
 static int dirtyrate_set_state(int *state, int old_state, int new_state)
 {
     assert(new_state < DIRTY_RATE_STATUS__MAX);

migration/dirtyrate.h

@@ -29,6 +29,12 @@
  */
 #define MIN_RAMBLOCK_SIZE                         128
 
+/*
+ * Take 1s as minimum time for calculation duration
+ */
+#define MIN_FETCH_DIRTYRATE_TIME_SEC              1
+#define MAX_FETCH_DIRTYRATE_TIME_SEC              60
+
 struct DirtyRateConfig {
     uint64_t sample_pages_per_gigabytes; /* sample pages per GB */
     int64_t sample_period_seconds; /* time duration between two sampling */