Linux patch reveals AMD's RDNA2 GPUs support Duty Cycle Scaling power management feature for ultraportable devices
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The guys over at Phoronix recently discovered an unannounced RDNA2 GPU feature in a recent Linux patch. Dubbed the Duty Cycle Scaling (DCS), this feature is supposedly supported by the RX 6800 series (Navi 21), as well as the upcoming Navi 22 (RX 6700 mid-range solutions) and especially Navi 23/24 (lower TDP solurions). Its purpose is to constantly monitor the core’s power / current / temperature and temporarily shut down the core for less than a microsecond when it is stressed too much, then turn it back as the power and temperature envelopes reset to normal parameters. This is designed to reduce power consumption and adhere to more strict TDP requirements usually found in “small power limit SKUs” equipping thin and light devices.
According to the Linux patch, DCS has two modes: Async and frame-aligned. The Async DCS mode shuts down the core based only on the thermal, current and power parameters, while the frame-aligned DCS mode may turn off the core after it successfully renders a frame on 3D fullscreen and VR workloads. The Linux driver only supports Async DCS for now, and it is specified that the ON and OFF time for the core is determined by the firmware according to the accumulated power credits. Additionally, the Linux driver mentions that DCS is different from the GFXOff capability, which is only used to shut the core down when idling.
This feature clearly is not needed for the mid-range and high-end desktop GPUs, but it could help laptops and ultraportables that come with restrictive dGPU TDPs. AMD has not yet announced any laptop version of the RDNA2 Navi 2x GPUs. However, we suspect these versions could be launched in Q2 2021.