BurstLink: Techniques for Energy-Efficient Video Display for Conventional and Virtual Reality Systems

ABSTRACTConventional planar video streaming is the most popular application in mobile systems. The rapid growth of 360° video content and virtual reality (VR) devices is accelerating the adoption of VR video streaming. Unfortunately, video streaming consumes significant system energy due to high power consumption of major system components (e.g., DRAM, display interfaces, and display panel) involved in the video streaming process. For example, in conventional planar video streaming, the video decoder (in the processor) decodes video frames and stores them in the DRAM main memory before the display controller (in the processor) transfers decoded frames from DRAM to the display panel. This system architecture causes large amount of data movement to/from DRAM as well as high DRAM bandwidth usage. As a result, DRAM by itself consumes more than 30% of the video streaming energy. We propose BurstLink, a novel system-level technique that improves the energy efficiency of planar and VR video streaming. BurstLink is based on two key ideas. First, BurstLink directly transfers a decoded video frame from the video decoder or the GPU to the display panel, completely bypassing the host DRAM. To this end, we extend the display panel with a double remote frame buffer (DRFB) instead of DRAM’s double frame buffer so that the system can directly update the DRFB with a new frame while updating the display panel’s pixels with the current frame stored in the DRFB. Second, BurstLink transfers a complete decoded frame to the display panel in a single burst, using the maximum bandwidth of modern display interfaces. Unlike conventional systems where the frame transfer rate is limited by the pixel-update throughput of the display panel, BurstLink can always take full advantage of the high bandwidth of modern display interfaces by decoupling the frame transfer from the pixel update as enabled by the DRFB. This direct and burst frame transfer of capability BurstLink significantly reduces energy consumption of video display by 1) reducing accesses to DRAM, 2) increasing system’s residency at idle power states, and 3) enabling temporal power gating of several system components after quickly transferring each frame into the DRFB. BurstLink can be easily implemented in modern mobile systems with minimal changes to the video display pipeline. We evaluate BurstLink using an analytical power model that we rigorously validate on an Intel Skylake mobile system. Our evaluation shows that BurstLink reduces system energy consumption for 4K planar and VR video streaming by 41% and 33%, respectively. BurstLink provides an even higher energy reduction in future video streaming systems with higher display resolutions and/or display refresh rates.