Why Did My Mobile Game’s FPS Crash? Uncovering Thermal Throttling on Galaxy S9+

During a monthly game performance regression test on a Galaxy S9+ device, developers observed a sharp and regular FPS decline: the frame rate dropped from around 50 FPS to the low teens after playing for a while, accompanied by a noticeable increase in jank.

Web‑based performance charts showed the same trend (see image below).

Initial analysis ruled out CPU overload (CPU usage stayed around 15 % with total usage near 40 %) and memory pressure (memory usage remained at a normal 500‑600 MB). GPU utilization dropped from about 80 % to 40 % during the FPS dip, but this was a consequence of the lower frame rate rather than a bottleneck.

Further investigation revealed that the device temperature rose dramatically, reaching around 70 °C, indicating severe heating. When the temperature exceeded the device’s thermal threshold, the CPU frequency throttled sharply—from 1700‑2800 MHz down to 576‑825 MHz—directly causing the FPS reduction.

This case demonstrates why mobile hardware incorporates thermal control mechanisms: to prevent overheating that could damage the CPU, manufacturers set temperature thresholds (often between 50 °C and 65 °C) that trigger frequency scaling. Understanding and monitoring these thresholds is essential for diagnosing performance issues.

Using the PerfDog platform, developers can collect comprehensive performance metrics—CPU, GPU, memory, FPS, temperature, and frequency—and correlate them to quickly pinpoint root causes like thermal throttling.