Approaching Vmin as an indicator of VRM quality
It is well known that a stable and even supply of the Vcore voltage is crucial for CPU overclocking. Small downward excursions during load changes can often cause instability, although the voltage may seem constant, at least according to software monitoring.
To be able to evaluate this without an oscilloscope, I use a static overclock of the P-cores at 5.0 GHz, the E-cores at 4.0 GHz and the cache or ring at 4.5 GHz. Prime95 with the Small-FFT preset and AVX2 are used as load. These values are chosen relatively conservatively in order to keep the waste heat within limits with a maximum of 85 °C core temperature, as this can also influence stability. For the best possible transient response during load changes, the highest LLC level 8 with the largest droop is selected.
The stability is now determined by the stability of the core voltage, which is lowered in the test until 30 minutes in Prime95 can no longer be managed stably. A Vcore voltage as low as possible, measured at the die of the CPU (die sense) is then the indicator for a good power supply. After all, even if we cannot record the actual minimum values (Vmin), the lowest possible average value conversely means smaller downward outliers.
Result is a minimum value of 1.022 V measured with HWinfo as “VR VOUT” of the PWM controller, resulting from 1.285 V set voltage with LLC8. Whether this is a good or a bad thing will have to be seen in the upcoming Z790 reviews. The CPU’s silicon quality, which is also crucial for this, must of course remain the same, which is why only this special CPU will be used in the future. The VRM components do not reach more than 61 °C in this endurance test in passive mode without helping airflow, which is quite respectable.
By the way, the motherboard rates this with CPU Force 2 with a value of 131 at a CPU temperature of 33 °C. Unfortunately, MSI’s silicon lottery prediction feature is still temperature- and thus cooler-dependent, but it at least allows a rough comparison between CPUs. Lower values are better here, by the way. For comparison, on an Asus motherboard this corresponds to an SP value of 103, where again higher is better.
Dynamic OC with fixed voltage and a twist
The dynamic overclocking of a CPU depending on the number of utilized cores is nothing new in the Z790 and the possible use of a variable voltage with the help of the AC_LL, DC_LL and LLC parameters already existed in the Z690. However, MSI has introduced an additional, new feature “Loadline Saturation” for the Z790 Godlike, which can effectively delay the start of the loadline sloap by a definable threshold of current in A.
Below this threshold, the power supply operates entirely without droop (LLC1), resulting in a constant, high voltage in low load situations. Only when the threshold is exceeded, the power supply switches to the defined LLC level (here 8) with the corresponding droop.
I use the feature here to achieve a dynamic overclocking with semi-static voltage. The P-cores of the CPU reach a maximum of 6.1 GHz and a minimum of 5.5 GHz depending on the load, the E-cores 4.5 to 4.2 GHz and the cache remains at the default of 4.5 to 4.9 GHz, with a set voltage of 1.43 V.
This setting is completely stable in Prime95 Small-FFT AVX2, no matter how many worker threads and which cores the workers are assigned to. With 1-2 cores loaded, the current remains below the load line saturation threshold of 40 A, which allows the VRM to keep the voltage at exactly 1.43 V here. Only when more than 2 cores are loaded does the PWM controller reach the saturation point and gradually droop the voltage to a minimum of 1.141 V. The resulting minimum voltage is slightly higher than without active load line saturation, since the current below the threshold is not included in the voltage droop calculation.
At least this is still the case now, according to MSI the behavior was not quite planned that way. Actually the minimum voltage at Set Voltage x and LLC Level y should always be identical, no matter if with or without Loadline Saturation. However, this will possibly be addressed in a BIOS update.
The dynamic overclocking up to 6.1 GHz that the Z790 Godlike enables with this is impressive and even though this would also be possible with the use of the CPU SVID, the implementation with static voltage and the new Loadline Saturation feature is an interesting alternative. As we know, upgrading a CPU power supply with still higher-quality components doesn’t add any value after a certain point. But the integration of new features to control the VRM even more precisely is even cooler and fits very well for an all-rounder mainboard like this one.
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