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mixin: Fix cpu usage graph #3109

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mixin: Fix cpu usage graph #3109

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7 changes: 1 addition & 6 deletions docs/node-mixin/lib/prom-mixin.libsonnet
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Original file line number Diff line number Diff line change
Expand Up @@ -66,17 +66,12 @@ local table = grafana70.panel.table;
datasource='$datasource',
span=6,
format='percentunit',
max=1,
min=0,
stack=true,
)
.addTarget(prometheus.target(
|||
(
(1 - sum without (mode) (rate(node_cpu_seconds_total{%(nodeExporterSelector)s, mode=~"idle|iowait|steal", instance="$instance", %(clusterLabel)s="$cluster"}[$__rate_interval])))
/ ignoring(cpu) group_left
count without (cpu, mode) (node_cpu_seconds_total{%(nodeExporterSelector)s, mode="idle", instance="$instance", %(clusterLabel)s="$cluster"})
)
(1 - sum without (mode) (rate(node_cpu_seconds_total{%(nodeExporterSelector)s, mode=~"idle|iowait|steal", instance="$instance", %(clusterLabel)s="$cluster"}[$__rate_interval])))
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@SuperQ SuperQ Sep 3, 2024 •
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I'm pretty sure we don't want to include iowait and steal here.

If we want this to be stacked CPU utilization, we probably want this:

Suggested change
(1 - sum without (mode) (rate(node_cpu_seconds_total{%(nodeExporterSelector)s, mode=~"idle|iowait|steal", instance="$instance", %(clusterLabel)s="$cluster"}[$__rate_interval])))
clamp(
avg without (mode) (
1-rate(node_cpu_seconds_total{%(nodeExporterSelector)s, mode="idle", instance="$instance", %(clusterLabel)s="$cluster"}[$__rate_interval])
),
0,
1
)

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I vaguely remember a discussion about steal. But I don't remember the details. (But it feels like I have included steal for a reason.)

Why would you also toss iowait? Isn't the whole idea here to find out if you don't utilize your CPUs for whatever reason, including being stuck waiting for IO?

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@SuperQ SuperQ Sep 3, 2024 •
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iowait is not CPU time. It's accounted for in CPU metrics but it's actually phantom time when nothing is done. You can have both 100% idle and 100% iowait Leading to -100% CPU use in this calculation.

I think this was an attempt to do what the kubernetes-mixin is doing, but it has the regexp inverted.

See: kubernetes-mixin/rules/node.libsonnet

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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/sched/cputime.c?id=HEAD#n222 looks more like the wait time is either added to idle or to iowait. But I'm just shooting in the dark here. Maybe that's not the relevant code, or it gets changed later on its way to node_exporter.

||| % config,
legendFormat='{{cpu}}',
intervalFactor=5,
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