International audienceMobile devices such as smart-phones and tablets are becoming the most important channel for delivering end-user Internet traffic especially multimedia content. One of the most popular multimedia application is video streaming. The video decoding process of this application is compute-intensive and is responsible of the consumption of a considerable part of the energy budget. Those mobile devices contain heterogeneous processing elements among-which we find Digital Signal Processors (DSP) and General Purpose Processors (GPP). In this context, the performance and energy estimation of those complex platforms is a difficult and time consuming task especially when considering both hardware and applicative parameters. In this paper, we propose a methodology for developing a unified high level video decoding performance and energy consumption analytical model for embedded heterogeneous platforms. This methodology is based on experimental measurements conducted on an embedded low-power platform. The developed model describes the performance and the energy consumption of H.264/AVC video decoding on both GPP and DSP in terms of video bit-rate, clock frequency and a set of comprehensive hardware and video related coefficients. It achieves a balance between a too abstract high level model and a detailed lower level one while guaranteeing a very good prediction properties (R-squared = 97%) for the tested videos. As a use case, we show that our model allows to accurately determine the bit-rate values for which video decoding on GPP is more energy-efficient than on DSP for a given platform
International audienceWe present in this paper GM-DVFS, an adaptive DVFS scheme for energy efficient decoding of H.264 videos. GM-DVFS uses metadata (normalized by the MPEG Green Metadata standard) providing information about the upcoming workload. In the solution we propose, these metadata are processed within an adaptive filter to build dynamically an accurate video decoding complexity model. This model serves to calculate the minimal required processor frequency for decoding a video frame while guaranteeing the real time constraints. Our performance evaluations showed that the proposed algorithm is able to converge to an accurate complexity model (4%) in less than 1 second (in the worst case). Moreover, it is simple to implement (250 lines of C code) and induces very low overhead (1400 cycles/frames). On the other hand, it allows to achieve up to 46% energy saving as compared to the on demand Linux DVFS governor
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