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Use floats for tracking cpu time. #563

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noncrab wants to merge 2 commits into from
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Use floats for tracking cpu time. #563

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f82fa41
Use a float gauge for tracking cpu time.
Mar 28, 2026
8bdd80b
Canary.
Mar 28, 2026
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23 changes: 7 additions & 16 deletions src/process_collector.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,9 +6,9 @@

use lazy_static::lazy_static;

use crate::counter::IntCounter;
use crate::counter::{Counter, IntCounter};
use crate::desc::Desc;
use crate::gauge::IntGauge;
use crate::gauge::{Gauge, IntGauge};
use crate::metrics::{Collector, Opts};
use crate::proto;

Expand All @@ -25,7 +25,7 @@ const METRICS_NUMBER: usize = 7;
pub struct ProcessCollector {
pid: pid_t,
descs: Vec<Desc>,
cpu_total: IntCounter,
cpu_total: Gauge,
open_fds: IntGauge,
max_fds: IntGauge,
vsize: IntGauge,
Expand All @@ -40,13 +40,8 @@ impl ProcessCollector {
let namespace = namespace.into();
let mut descs = Vec::new();

let cpu_total = IntCounter::with_opts(
Opts::new(
"process_cpu_seconds_total",
"Total user and system CPU time spent in \
seconds.",
)
.namespace(namespace.clone()),
let cpu_total = Gauge::with_opts(
Opts::new("process_cpu_seconds_total", "TEST.").namespace(namespace.clone()),
)
.unwrap();
descs.extend(cpu_total.desc().into_iter().cloned());
Expand Down Expand Up @@ -163,12 +158,8 @@ impl Collector for ProcessCollector {
self.rss.set((stat.rss as i64) * *PAGESIZE);

// cpu
let total = (stat.utime + stat.stime) / *CLK_TCK as u64;
let past = self.cpu_total.get();
// If two threads are collecting metrics at the same time,
// the cpu_total counter may have already been updated,
// and the subtraction may underflow.
self.cpu_total.inc_by(total.saturating_sub(past));
let total = (stat.utime + stat.stime) as f64 / *CLK_TCK as f64;
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@noncrab noncrab Mar 28, 2026

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As noted in the description, I'm not quite sure how to represent the risks of precision loss here. Is it worth noting?

self.cpu_total.set(total);
cpu_total_mfs = Some(self.cpu_total.collect());

// threads
Expand Down