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Most CI runners are the wrong size

40% of jobs we see average under 30% CPU utilization. Another 12% are pinned at 100% on the critical path.

Priya Raghavan · Infrastructure · 2026-06-03 · 6 min read

Runner size is usually chosen once, defensively, and never revisited. Utilization data says that choice is wrong in both directions more often than it is right.

Oversized: 40% of jobs

Average CPU utilization under 30% means you are paying for cores that sit idle. The most common cause is a job that was moved to a bigger runner to fix a problem that turned out to be cache-related.

Undersized: 12% of jobs

Pinned at 100% for the whole job, and on the critical path. Here a larger runner pays for itself immediately in developer waiting time, even at a higher per-minute rate.

The third category

High I/O wait with low CPU. These jobs are disk-bound, and no amount of extra cores will help. They need faster storage.

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