Dell XPS 15 9570: 15 % more performance by undervolting
We already reviewed the entry-level SKU of the new Dell XPS 9570 with the Coffee Lake quad-core processor. The cooling solution did not have big issues with the smaller processor, so we were eager to find out how it handles the faster hexa-core CPU. We are testing a unit with the Core i7-8750H right now and already performed some benchmarks.
Dell increased the power limits of the processor. As long as the temperature is not too high, the short-term consumption can be as high as 78W (for 28 seconds) and 56W for sustained load. We can observe up to 71W during the start of Cinebench R15, but not all the cores reach the maximum frequency of 3.9 GHz. The clock has to be reduced towards the end of the Cinebench run due to the temperature, but 6x 3.3-3.4 GHz (56W) is still decent. The first result is very good, but the scores drop is subsequent runs and eventually level off at around 1,000 points during our Cinebench Multi loop, which is also shown by the red graph below.
We reduced the core voltage of the CPU with the tool Intel XTU and refer to our dedicated article for detailed instructions. Attention: You can affect the system stability if you are not careful. Every processor is slightly different, so you cannot just use our value. Notebookcheck does not assume any liabilities for potential damages.
We were able to run the Core i7-8750H at -0.115 V, which means the processor temperature is not as high at high clocks and this improves the performance. The first Cinebench results is just slightly faster, but the score levels off at more than 1150 points over the course of the Cinebench loop, so you get more than 15 % more performance under sustained workloads.
| Default | -0.115 V | |
|---|---|---|
| Clock | ~3.2 GHz | ~3.6 GHz |
| Temperature | ~82.5 °C | ~83 °C |
| Power consumption | ~45 Watts | ~50 Watts |
The diagram shows the CPU can maintain 56W after a spike, which is not always the case with the default settings. The average core clock is 400 MHz higher at the same time, which requires a bit more power, but the core temperature is basically identical.
The CPU now consumes up to 76W for the full 6x 3.9 GHz, and 56W for a steady 6x 3.7 GHz. This shows how inefficient the current CPU generation is at these clocks, because 6x 200 MHz more require 20 Watts more. The advantages of the voltage reduction are not just limited to sustained workloads. Short peak load is more common in practice, and the temperature will stay lower so the cooling unit does not spin up as quickly or can stay turned off, respectively.
