[ovs-dev] [PATCH] dpif-netdev: fix meter granulariy.

[William Tu]

When testing packet rate around 1Mpps with meter enabled, the frequency
of hitting meter action becomes much higher, around 30us each time.
As a result, the meter's calculation of 'uint32_t delta_t' becomes
always 0 and meter action has no effect.  This is due to the previous
commit 05f9e707e194 divides the delta by 1000, in order to convert to
msec granularity.  The patch fixes it by using double to hold the delta
value.

Fixes: 05f9e707e194 ("dpif-netdev: Use microsecond granularity.")
Cc: Ilya Maximets <i.maximets at samsung.com>
Cc: Yi-Hung Wei <yihung.wei at gmail.com>
Signed-off-by: William Tu <u9012063 at gmail.com>
---
 lib/dpif-netdev.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 4d6d0c372236..61d0e9f2bf69 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -5525,8 +5525,8 @@ dp_netdev_run_meter(struct dp_netdev *dp, struct dp_packet_batch *packets_,
     struct dp_meter *meter;
     struct dp_meter_band *band;
     struct dp_packet *packet;
-    long long int long_delta_t; /* msec */
-    uint32_t delta_t; /* msec */
+    double double_delta_t; /* msec */
+    double delta_t; /* msec */
     const size_t cnt = dp_packet_batch_size(packets_);
     uint32_t bytes, volume;
     int exceeded_band[NETDEV_MAX_BURST];
@@ -5549,12 +5549,12 @@ dp_netdev_run_meter(struct dp_netdev *dp, struct dp_packet_batch *packets_,
     memset(exceeded_rate, 0, cnt * sizeof *exceeded_rate);
 
     /* All packets will hit the meter at the same time. */
-    long_delta_t = (now - meter->used) / 1000; /* msec */
+    double_delta_t = (double)(now - meter->used) / 1000.0; /* msec */
 
     /* Make sure delta_t will not be too large, so that bucket will not
      * wrap around below. */
-    delta_t = (long_delta_t > (long long int)meter->max_delta_t)
-        ? meter->max_delta_t : (uint32_t)long_delta_t;
+    delta_t = (double_delta_t > (long long int)meter->max_delta_t)
+        ? (double)meter->max_delta_t : double_delta_t;
 
     /* Update meter stats. */
     meter->used = now;
-- 
2.7.4