Fixed inaccurate 'node_network_speed_bytes' when speeds are low (#1580)

Integer division and the order of operations when converting Mbps to Bps
results in a loss of accuracy if the interface speeds are set low.
e.g. 100 Mbps is reported as 12000000 Bps, should be 12500000
     10 Mbps is reported as 1000000 Bps, should be 1250000

Signed-off-by: Thomas Lin <t.lin@mail.utoronto.ca>

CHANGELOG.md

@@ -34,6 +34,7 @@
 * [BUGFIX] Strip path.rootfs from mountpoint labels #1421
 * [BUGFIX] Fix empty string in path.rootfs #1464
 * [BUGFIX] Fix typo in cpufreq metric names #1510
+* [BUGFIX] Fix network speed math #1580
 
 ## 0.18.1 / 2019-06-04
 

collector/netclass_linux.go

@@ -144,7 +144,7 @@ func (c *netClassCollector) Update(ch chan<- prometheus.Metric) error {
 		}
 
 		if ifaceInfo.Speed != nil {
-			speedBytes := int64(*ifaceInfo.Speed / 8 * 1000 * 1000)
+			speedBytes := int64(*ifaceInfo.Speed * 1000 * 1000 / 8)
 			pushMetric(ch, c.subsystem, "speed_bytes", speedBytes, ifaceInfo.Name, prometheus.GaugeValue)
 		}