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Correct CPU usage calculation in presence of offline CPUs and newer Linux 

In https://github.com/torvalds/linux/commit/5ca3726 (released in v4.7-rc1) the
content of the `cpuacct.usage_percpu` file in sysfs was changed to include both
online and offline cpus. This broke the arithmetic in the stats helpers used by
`docker stats`, since it was using the length of the PerCPUUsage array as a
proxy for the number of online CPUs.

Add current number of online CPUs to types.StatsJSON and use it in the
calculation.

Keep a fallback to `len(v.CPUStats.CPUUsage.PercpuUsage)` so this code
continues to work when talking to an older daemon. An old client talking to a
new daemon will ignore the new field and behave as before.

Fixes #28941.

Signed-off-by: Ian Campbell <ian.campbell@docker.com>
This commit is contained in:
Ian Campbell 2017-03-06 17:29:09 +00:00
parent 78c204ef79
commit 54a5077ca5
1 changed files with 5 additions and 1 deletions
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6
command/container/stats_helpers.go
View File

@ -178,10 +178,14 @@ func calculateCPUPercentUnix(previousCPU, previousSystem uint64, v *types.StatsJ
cpuDelta = float64(v.CPUStats.CPUUsage.TotalUsage) - float64(previousCPU)
// calculate the change for the entire system between readings
systemDelta = float64(v.CPUStats.SystemUsage) - float64(previousSystem)
onlineCPUs = float64(v.CPUStats.OnlineCPUs)
)
if onlineCPUs == 0.0 {
onlineCPUs = float64(len(v.CPUStats.CPUUsage.PercpuUsage))
}
if systemDelta > 0.0 && cpuDelta > 0.0 {
cpuPercent = (cpuDelta / systemDelta) * float64(len(v.CPUStats.CPUUsage.PercpuUsage)) * 100.0
cpuPercent = (cpuDelta / systemDelta) * onlineCPUs * 100.0
}
return cpuPercent
}