fix(core): establish cpu baseline when possible to improve measurement accuracy

[leosvelperez]

Current Behavior

New task processes show 0% CPU on their first measurement because no baseline exists. Accurate readings only appear on the second collection cycle (~1s later).

Expected Behavior

New task processes get accurate CPU readings on their first measurement. The collector establishes CPU baselines for newly registered processes ~250ms before collection, giving sysinfo enough time to calculate accurate CPU deltas.

Technical Details: Baselining & Collection Flow

The collection loop runs in 4 phases:

 T=0ms      T=750ms      T=1000ms    T=1750ms     T=2000ms  
   |           |             |           |            |
   v           v             v           v            v
Collect → Sleep(750ms) → Baseline → Sleep(250ms) → Collect → ...

1. Collect: Refresh all processes and gather metrics
2. Post-collection sleep: Wait until baseline time (interval - 250ms)
3. Baseline: Bulk CPU refresh for newly registered PIDs (if any)
4. Pre-collection sleep: Wait 250ms for accurate CPU delta calculation

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Project	Deployment	Review	Updated (UTC)
nx-dev	Ready	Preview	Jan 19, 2026 1:50pm

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☁️ Nx Cloud last updated this comment at 2026-01-19 16:16:30 UTC

[nx-cloud]

Important

At least one additional CI pipeline execution has run since the conclusion below was written and it may no longer be applicable.

Nx Cloud is proposing a fix for your failed CI:

We removed the pre-loop baseline logic that was interfering with process initialization. The original code ran a baseline refresh immediately at startup (T=0ms), then performed the first collection only 250ms later, which disrupted normal task process startup and caused the Playwright webserver readiness check to timeout. By letting the first collection happen immediately (as before the PR) and moving baseline establishment to occur after the first collection, we maintain backward compatibility with existing process startup expectations while preserving the PR's intent of accurate CPU measurements through strategic baseline timing.

We could not verify this fix.

diff --git a/packages/nx/src/native/metrics/collector.rs b/packages/nx/src/native/metrics/collector.rs
index 01c5288b44..4d2671092e 100644
--- a/packages/nx/src/native/metrics/collector.rs
+++ b/packages/nx/src/native/metrics/collector.rs
@@ -145,13 +145,7 @@ impl CollectionRunner {
         let interval = Duration::from_millis(self.config.collection_interval_ms);
         // sysinfo's MINIMUM_CPU_UPDATE_INTERVAL + 50ms safety buffer
         let baseline_offset = sysinfo::MINIMUM_CPU_UPDATE_INTERVAL + Duration::from_millis(50);
-        let post_collection_sleep = interval - baseline_offset;
-
-        // First iteration: baseline if needed, then wait before first collection
-        if self.should_collect.load(Ordering::Acquire) && self.run_baseline_if_needed() {
-            // Sleep to allow CPU to be calculated correctly for the baselined processes
-            self.sleep_with_early_exit(baseline_offset);
-        }
+        let post_collection_sleep = interval.saturating_sub(baseline_offset);
 
         while self.should_collect.load(Ordering::Acquire) {
             // Collect current metrics and send to main collector thread
@@ -166,6 +160,7 @@ impl CollectionRunner {
                 break;
             }
 
+            // Establish baselines for newly registered processes if any
             self.run_baseline_if_needed();
             // Sleep until next collection (offset)
             self.sleep_with_early_exit(baseline_offset);

  

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