dpif-netdev: includes microsecond delta in meter bucket calculation

When dp-netdev meter rate is higher than 200Mbps, observe
more than 10% bias from configured rate value with UDP traffic.

In dp-netdev meter, millisecond delta between now and last used
is taken into bucket size calcualtion, while sub-millisecond part
is truncated.

If traffic rate is pretty high, time delta can be few milliseconds,
its ratio to truncated part is less than 10:1, the loss of bucket
size caused by truncated can be observed obviously by commited
traffic rate.

In this patch, microsend delta part is included in calculation
of meter bucket to make it more precise.

Signed-off-by: Jiang Lidong <[email protected]>
Signed-off-by: William Tu <[email protected]>

lib/dpif-netdev.c

@@ -5735,6 +5735,7 @@ dp_netdev_run_meter(struct dp_netdev *dp, struct dp_packet_batch *packets_,
     struct dp_packet *packet;
     long long int long_delta_t; /* msec */
     uint32_t delta_t; /* msec */
+    uint32_t delta_in_us; /* usec */
     const size_t cnt = dp_packet_batch_size(packets_);
     uint32_t bytes, volume;
     int exceeded_band[NETDEV_MAX_BURST];
@@ -5765,6 +5766,9 @@ dp_netdev_run_meter(struct dp_netdev *dp, struct dp_packet_batch *packets_,
            Assuming that all racing threads received packets at the same time
            to avoid overflow. */
         long_delta_t = 0;
+        delta_in_us  = 0;
+    } else {
+        delta_in_us  = (now - meter->used) % 1000;
     }
 
     /* Make sure delta_t will not be too large, so that bucket will not
@@ -5800,6 +5804,7 @@ dp_netdev_run_meter(struct dp_netdev *dp, struct dp_packet_batch *packets_,
 
         /* Update band's bucket. */
         band->bucket += delta_t * band->up.rate;
+        band->bucket += delta_in_us * band->up.rate / 1000;
         if (band->bucket > band->up.burst_size) {
             band->bucket = band->up.burst_size;
         }