Off-chip latency-driven dynamic voltage and frequency scaling for an MPEG decoding

  • Authors:
  • Kihwan Choi;Ramakrishna Soma;Massoud Pedram

  • Affiliations:
  • University of Southern California, Los Angeles, CA;University of Southern California, Los Angeles, CA;University of Southern California, Los Angeles, CA

  • Venue:
  • Proceedings of the 41st annual Design Automation Conference
  • Year:
  • 2004

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Abstract

This paper describes a dynamic voltage and frequency scaling (DVFS) technique for MPEG decoding to reduce the energy consumption using the computational workload decomposition. This technique decomposes the workload for decoding a frame into on-chip and off-chip workloads. The execution time required for the on-chip workload is CPU frequency-dependent, whereas the off-chip workload execution time does not change, regardless of the CPU frequency, resulting in the maximum energy savings by setting the minimum frequency during off-chip workload execution time, without causing any delay penalty. This workload decomposition is performed using a performance-monitoring unit (PMU) in the XScale-processor, which provides various statistics such as cache hit/miss and CPU stall, due to data dependency at run time. The on-chip workload for an incoming frame is predicted using a frame-based history so that the processor voltage and frequency can be scaled to provide the exact amount of computing power needed to decode the frame. To guarantee a quality of service (QoS) constraint, a prediction error compensation method, called inter-frame compensation, is proposed in which the on-chip workload prediction error is diffused into subsequent frames such that run time frame rates change smoothly. The proposed DVFS algorithm has been implemented on an XScale-based Testbed. Detailed current measurements on this platform demonstrate significant CPU energy savings ranging from 50% to 80% depending on the video clip.