hw/acpi/piix4: Move TYPE_PIIX4_PM to a public header

[qemu.git] / include / qemu / ratelimit.h

diff --git a/include/qemu/ratelimit.h b/include/qemu/ratelimit.h
index d413a4a696b78f79628e459395bb87dd35d681c1..1b38291823b7fef5ac596557b0269f0c38b8887a 100644 (file)
--- a/include/qemu/ratelimit.h
+++ b/include/qemu/ratelimit.h
@@ -12,37 +12,62 @@
  */
 
 #ifndef QEMU_RATELIMIT_H
-#define QEMU_RATELIMIT_H 1
+#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 @n data units (where @n matches the scale chosen
+ * during ratelimit_set_speed). 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);
+    double 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. Wait based on the excess amount and then start a new
+     * slice. */
+    delay_slices = (double)limit->dispatched / limit->slice_quota;
+    limit->slice_end_time = limit->slice_start_time +
+        (uint64_t)(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