diff mbox

[dpdk-dev,v1] lib/bitratestats: fix integer roundoff

Message ID 1492608408-12084-1-git-send-email-remy.horton@intel.com (mailing list archive)
State Accepted, archived
Headers

Checks

Context Check Description
ci/checkpatch success coding style OK
ci/Intel-compilation success Compilation OK

Commit Message

Remy Horton April 19, 2017, 1:26 p.m. UTC 
  In the absence of traffic, it is possible for the bitrate moving average
to get stuck at a non-zero value, due to the calculated delta being less
than what an integer can represent.

Fixes: 2ad7ba9a6567 ("bitrate: add bitrate statistics library")

Signed-off-by: Remy Horton <remy.horton@intel.com>
---
 lib/librte_bitratestats/rte_bitrate.c | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

Thomas Monjalon April 20, 2017, 11:09 p.m. UTC | #1 
19/04/2017 15:26, Remy Horton:
> In the absence of traffic, it is possible for the bitrate moving average
> to get stuck at a non-zero value, due to the calculated delta being less
> than what an integer can represent.
> 
> Fixes: 2ad7ba9a6567 ("bitrate: add bitrate statistics library")
> 
> Signed-off-by: Remy Horton <remy.horton@intel.com>

Applied, thanks

PS: please not that the title of this patch does not match
the title of the fixed patch.
Changed to "bitrate: fix integer roundoff"
diff mbox

Patch

diff --git a/lib/librte_bitratestats/rte_bitrate.c b/lib/librte_bitratestats/rte_bitrate.c
index 260750f..193aa69 100644
--- a/lib/librte_bitratestats/rte_bitrate.c
+++ b/lib/librte_bitratestats/rte_bitrate.c
@@ -118,6 +118,11 @@  rte_stats_bitrate_calc(struct rte_stats_bitrates *bitrate_data,
 	else
 		delta = (delta * alpha_percent - 50) / 100;
 	port_data->ewma_ibits += delta;
+	/* Integer roundoff prevents EWMA between 0 and (100/alpha_percent)
+	 * ever reaching zero in no-traffic conditions
+	 */
+	if (cnt_bits == 0 && delta == 0)
+		port_data->ewma_ibits = 0;
 	port_data->mean_ibits = cnt_bits;
 
 	/* Outgoing bitrate (also EWMA) */
@@ -132,6 +137,8 @@  rte_stats_bitrate_calc(struct rte_stats_bitrates *bitrate_data,
 	else
 		delta = (delta * alpha_percent - 50) / 100;
 	port_data->ewma_obits += delta;
+	if (cnt_bits == 0 && delta == 0)
+		port_data->ewma_obits = 0;
 	port_data->mean_obits = cnt_bits;
 
 	values[0] = port_data->ewma_ibits;