Discussion on Power Limit Throttling
Discussion on Power Limit Throttling
Hi, your laptop runs an i5-8250U processor. After using Intel XTU for undervolting, your CPU stress test now shows a peak frequency of 3.03 GHz and package temp stays at 64°C. However, it still doesn’t consistently hit 3.4 GHz even with full load. The power limit is also throttling when frequencies drop. Let me know if you need more guidance.
Which stress test applies? The 8250U supports a maximum of 15 Watts of TDP. By default, Intel built this CPU to reduce performance when reaching that power threshold during extended testing. Intel XTU indicates this behavior. Have you checked the two turbo power limits in XTU? Have you experimented with adjusting them? Raising both short and long power limits could potentially extend your CPU's runtime or eliminate throttling issues entirely.
I adjusted the settings based on the results from XTU and Prime95. The recommended range is typically at the upper limit, but you should monitor your system closely. It’s safe to push toward the maximum if stability allows, though performance might be affected.
Intel's low power U series CPUs aren't meant for high-speed stress testing such as Prime95 or the XTU test at full capacity. They have a 15 Watt TDP rating. To maintain that power level during these tests, the processor reduces its speed and slows down. It may happen but is unlikely. If you're concerned about damaging your laptop, avoid running Prime95 overnight. For better performance, consider increasing the turbo power limits—try 20 or 25 Watts instead of 15. Monitor your CPU temperature. As long as the heatsink and fan work properly and the CPU stays cool, everything should be fine. Some laptops with these CPUs have a strict 15 Watt limit set by Intel. Changing the turbo settings that XTU allows might not exceed 15 Watts, but it's worth testing. Lenovo left my 8th Gen U series CPU unlocked, allowing it to run well beyond its 15 Watt limit indefinitely or until it overheats.
I believe my laptop is hitting its capacity. I observed that whenever the power throttling occurs at full utilization, the package TDP reduces to 10W (maximum 13W). The average temperature stayed within a 2-3°C range. I adjusted the turbo boost limits to 25W and set both maximum and minimum short boost values. It appears the frequency rose by about 5%. Regardless, the undervolted CPU still performs better than the standard one.
Intel TurboBoost enables these energy-efficient CPUs to function effectively. A peak of 3.4 GHz is the upper limit for one core under heavy workloads. For a U-class processor, Intel usually reduces the overall maximum speed when all cores are active. This happens because running two cores together consumes twice the power compared to using just one. When you don’t utilize all cores, there’s extra power margin that allows a single core to operate at a higher frequency. To truly observe the 3.4 GHz capability, start Windows with a single thread and trigger a benchmark test.
@svmlegacy Several Intel processors adjust turbo speeds based on active cores. The 8250U stands apart—it can utilize the complete 34 multiplier regardless of whether one, two, three, or all four cores are running. Intel uses lower power caps to manage these chips, keeping the turbo settings unchanged. Which laptop are you using? Dell and HP generally restrict most low-power models, while Lenovo and others keep their maximum limits open. The Intel XTU model doesn’t support this flexibility. To access higher limits, switch from XTU to ThrottleStop, which offers a feature in its FIVR window called Disable and Lock Turbo Power Limits. This adjustment has significantly improved performance for many devices.
I'm using an Acer Swift 3 (SF315-52G). The newest XTU release didn't work with my laptop, so I downloaded an older version from a community source. I've tried the ThrottleStop, but I'm not very clear on how it works, though I still have it installed.