Formal online methods for voltage/frequency control in multiple clock domain microprocessors

Abstract

Multiple Clock Domain (MCD) processors are a promising future alternative to today's fully synchronous designs. Dynamic Voltage and Frequency Scaling (DVFS) in an MCD processor has the extra flexibility to adjust the voltage and frequency in each domain independently. Most existing DVFS approaches are profile-based offline schemes which are mainly suitable for applications whose execution char-acteristics are constrained and repeatable. While some work has been published about online DVFS schemes, the prior approaches are typically heuristic-based. In this paper, we present an effective online DVFS scheme for an MCD processor which takes a formal analytic approach, is driven by dynamic workloads, and is suitable for all applications. In our approach, we model an MCD processor as a queue-domain network and the online DVFS as a feedback control problem with issue queue occupancies as feedback signals. A dynamic stochastic queuing model is first proposed and linearized through an accu-rate linearization technique. A controller is then designed and verified by stability analysis. Finally we evaluate our DVFS scheme through a cycle-accurate simulation with a broad set of applications selected from MediaBench and SPEC2000 benchmark suites. Compared to the best-known prior approach, which is heuristic-based, the proposed online DVFS scheme is substantially more effective due to its automatic regulation ability. For example, we have achieved a 2-3 fold increase in efficiency in terms of energy-delay product improvement. In addition, our control theoretic technique is more resilient, requires less tuning effort, and has better scalability as compared to prior online DVFS schemes.We believe that the techniques and methodology described in this paper can be generalized for energy control in processors other than MCD, such as tiled stream processors.

An Overview of Architecture-Level Power- and Energy-Efficient Design Techniques

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“…Interestingly, their online control-theoretic approach is able to achieve a full 85.5% of the EDP improvement offered by the prior off-line scheduling approach. Wu et al [23] extend the online approach using formal control theory and a dynamic stochastic model based on input-queue occupancy for the MCDs.…”

Efficient microarchitecture policies for accurately adapting to power constraints

“…Based on the fact that power consumption depends on both voltage and frequency (P V DD 2 f), DVFS dynamically scales these terms to save power [6][7] [16]. Unfortunately, one of the major concerns about DVFS has been the slow off-chip voltage regulators that lack the ability to adjust to different voltages at small time scales (0.016mV / ns according to [7]). Modern real implementations are limited to temporary coarse-grained adjustments governed by runtime software (i.e., the OS).…”

State observer controller design for packets flow control in networks-on-chip

“…For a control process where the data is processed by a single IP core, the knowledge of input and output parameters is essential. A proportional-integral-derivative (PID) controller is the best solution in such cases [18]. But when the data is processed by hundreds of IP cores, not only the knowledge of input and output parameters, but also that of intermediate states is essential.…”