1 files changed, 34 insertions, 9 deletions

diff --git a/include/qemu/ratelimit.h b/include/qemu/ratelimit.h
index 1e3cb13b28..8da1232574 100644
--- a/include/qemu/ratelimit.h
+++ b/include/qemu/ratelimit.h
@@ -15,34 +15,59 @@
 #define QEMU_RATELIMIT_H
 
 typedef struct {
-    int64_t next_slice_time;
+    int64_t slice_start_time;
+    int64_t slice_end_time;
     uint64_t slice_quota;
     uint64_t slice_ns;
     uint64_t dispatched;
 } RateLimit;
 
+/** Calculate and return delay for next request in ns
+ *
+ * Record that we sent @p n data units. If we may send more data units
+ * in the current time slice, return 0 (i.e. no delay). Otherwise
+ * return the amount of time (in ns) until the start of the next time
+ * slice that will permit sending the next chunk of data.
+ *
+ * Recording sent data units even after exceeding the quota is
+ * permitted; the time slice will be extended accordingly.
+ */
 static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
 {
     int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
+    uint64_t delay_slices;
 
-    if (limit->next_slice_time < now) {
-        limit->next_slice_time = now + limit->slice_ns;
+    assert(limit->slice_quota && limit->slice_ns);
+
+    if (limit->slice_end_time < now) {
+        /* Previous, possibly extended, time slice finished; reset the
+         * accounting. */
+        limit->slice_start_time = now;
+        limit->slice_end_time = now + limit->slice_ns;
         limit->dispatched = 0;
     }
-    if (limit->dispatched == 0 || limit->dispatched + n <= limit->slice_quota) {
-        limit->dispatched += n;
+
+    limit->dispatched += n;
+    if (limit->dispatched < limit->slice_quota) {
+        /* We may send further data within the current time slice, no
+         * need to delay the next request. */
         return 0;
-    } else {
-        limit->dispatched = n;
-        return limit->next_slice_time - now;
     }
+
+    /* Quota exceeded. Calculate the next time slice we may start
+     * sending data again. */
+    delay_slices = (limit->dispatched + limit->slice_quota - 1) /
+        limit->slice_quota;
+    limit->slice_end_time = limit->slice_start_time +
+        delay_slices * limit->slice_ns;
+    return limit->slice_end_time - now;
 }
 
 static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
                                        uint64_t slice_ns)
 {
     limit->slice_ns = slice_ns;
-    limit->slice_quota = ((double)speed * slice_ns)/1000000000ULL;
+    limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1);
 }
 
 #endif