Hi, I just had a look at the power readings of one of our GeForce 1080 cards using nvidia-smi and noticed that the power draw occasionally goes significantly above the “Enforced Power Limit” parameter.
I’ve seen the card draw nearly 218 W of power while “Enforced Power Limit” is set to it’s default value of 180 W. If increasing “Enforced Power Limit” to it’s maximum value of 217 W, I’ve seen the nvidia-smi report power draws up to 229 W.
Are these values “higher than max” values simply measurement flukes, or is there a better explanation?
The power limit put in place by the GPU power supply is essentially a combination of clocks and voltage.
When the observed power is seen to go above the power limit, then the clocks will be reduced, to reduce power draw.
So it’s possible for short excursions above the power limit. These will be “short” because the monitoring system will move the GPU to a lower performance state (lower clocks) to reduce the power draw based on the workload, when the observed power exceeds the limit. But it’s not an instantaneous clamp on the power draw.
In addition to what txbob says (non-instantaneous response of the power regulating mechanism), one should keep in mind that the sensors one might typically find in these kind of products should not be assumed to have better than +/-5% accuracy.
Short power surges of the magnitude observed here should not be cause for concern as both on-board voltage regulators and system power supply units are designed with engineering margin to be able to absorb these. Short spikes also don’t contribute meaningfully to overall (long-term) power consumption.
My general recommendation for high performance operation of GPUs is to operate them at the maximum power limit allowed by the GPU to avoid throttling. This assumes proper sizing of the system PSU, which should be chosen such that the nominal total wattage of all components adds to around 50%-60% of nominal PSU output wattage, so there are ample reserves and the PSU operates at peak efficiency. PSUs rated 80 PLUS Platinum or at least 80 PLUS Gold are preferable.
Thanks, that makes sense.