stochastic current prediction enabled frequency actuator for runtime resonance noise reduction

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Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction Yiyu Shi*, Jinjun Xiong + , Howard Chen + and Lei He* *Electrical Engineering Dept., University of California, Los Angeles + IBM T. J. Watson Research Center, Yorktown Heights, NY This paper is supported in part by an NSF CAREER award CCR0306682 and a UC MICRO grant sponsored by Actel and Fujitsu.

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Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction. Yiyu Shi*, Jinjun Xiong + , Howard Chen + and Lei He* *Electrical Engineering Dept., University of California, Los Angeles + IBM T. J. Watson Research Center, Yorktown Heights, NY - PowerPoint PPT Presentation

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Page 1: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise ReductionStochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Yiyu Shi*, Jinjun Xiong+, Howard Chen+ and Lei He**Electrical Engineering Dept., University of California, Los Angeles

+IBM T. J. Watson Research Center, Yorktown Heights, NY

This paper is supported in part by an NSF CAREER award

CCR0306682 and a UC MICRO grant sponsored by Actel and Fujitsu.

Page 2: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

OutlineOutline

Background on Resonance Noise

Algorithm

Experimental Results

Conclusions

Page 3: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Power Supply Noise AnalysisPower Supply Noise Analysis

resonance between on-chip capacitance and package inductance

frequency

H(jw)

resonance frequency fres

~100MHz

ω0

I(jw)

Page 4: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Important Characteristics of Resonance NoiseImportant Characteristics of Resonance Noise

Resonance noise is significant when the spectrum of load current has harmonic components close to the resonance frequency.

It can be reduced by changing the spectrum of the load current such as changing the voltage or clock frequency

Usually occurs at a frequency (50MHz~200MHz) much lower than the clock frequency (GHz)

Usually occurs during certain instruction loops at runtime and is hard to detect during design-time. It is impossible to cover the whole operation space

It is difficult to design a network that is reliable to multiple applications

Page 5: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Design stage techniques or runtime techniques?Design stage techniques or runtime techniques?

There are many existing approaches for high frequency noise reduction at the design stage P/G network sizing [Tan:DAC’99] Topology optimization [Erhard:DAC’92] Decap budgeting [Shi:Iccad’07] Decoupling trench capacitance [Garofano’07]

However, to suppress the resonance noise effectively, we have to do it at runtime such as Band-limited damping [Xu:ISSCC’07] On-chip voltage regulator [Ang:ISSCC’00] Single-shot transient suppressor

Page 6: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Retroactive or Proactive?Retroactive or Proactive?

All the existing runtime techniques are retroactive They can only function after the noise increases above the

tolerance threshold

It takes quite a long time for the circuit to respond to the noise

A better approach can be to suppress the noise before it actually happens (proactively) Accurate and efficient prediction of the load currents in the future

Runtime adjustment based on the prediction results.

In this paper, we use the clock frequency actuator Adjust clock frequency dynamically to avoid resonance

frequency

Page 7: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Resonance Noise Suppression by Frequency ActuatorResonance Noise Suppression by Frequency Actuator

frequency

H(jw)

resonance frequency fres ~100MHz

ω0

I(jw)

ω1

Page 8: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

OutlineOutline

Background on Resonance Noise

Algorithm

Experimental Results

Conclusions

Page 9: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Overview of the algorithmOverview of the algorithm

We gather the current data from the on-chip dynamic current sensors. The load currents are modeled as triangular waveforms with uniform rising

and falling time. Only peak value of the currents need to be recorded.

Based on the data, we can apply linear filter and predict the load current in the coming a few clock cycles. We use two kinds of filters (predetermined linear filter and adaptive filter)

to allow tradeoff between accuracy and hardware cost.

Together with the RLC model of the P/G network and package, we can compute the noise profile at all ports.

Decide the optimal frequency according to the predicted load currents to minimize the harmonic component at resonance frequency

Page 10: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Predetermined FilterPredetermined Filter

We model the peak currents as a generalized Markov stochastic process over different clock cycles.

At clock cycle k, given M peak current data with L clock cycles interval Ik, Ik-L, Ik-2L, Ik-3L, … Ik-ML, we want to predict the peak current L clock cycles ahead

From the field of signal processing, we have

Predetermined filter has smaller complexity to build. It has larger prediction error, but with guaranteed convergence.

To improve accuracy, we may adjust ψi dynamically at runtime

iLk

M

iiLk II

1

0

ˆ

filter coefficients obtained from training data

LkI ˆ

Adaptive filter

Page 11: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Adaptive FilterAdaptive Filter

Ik-L, Ik-2L, …., Ik-ML are the history peak current data

Ik is the predicted peak current

Ψ1, k-1, Ψ2, k-1, …, ΨM, k-1 are the adaptive filter coefficient

δΨ1, k-1, δΨ2, k-1, …, δΨM, k-1 are the correction for the adaptive filter coefficient

Adaptive filter is more complex. It has less prediction error, but may not converge.

Page 12: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Optimal Frequency SelectionOptimal Frequency Selection

We can predict peak currents in future L-1 clock cycles using the history data in M*L clock cycles by the two filters as

The detailed current waveform can then be recovered under the triangular waveform assumption as

The optimal clock frequency T can then be determined in two steps First analyze the spectrum of u(t) for each permissible clock period T Then select the one that has minimum value at the resonance frequency.

unit triangular waveform

Page 13: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

OutlineOutline

Background on Resonance Noise

Algorithm

Experimental Results

Conclusions

Page 14: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Current Prediction ResultsCurrent Prediction Results

LMS adaptive prediction has less prediction error in general

Predetermined filter can always guarantee the convergence

Page 15: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Resonance Noise Reduction ComparisonResonance Noise Reduction Comparison

Compared with the baseline model without frequency actuator the retroactive approach can only reduce the max noise by up to 14%

and reduce the mean noise by up to 33%

our proactive approach with predetermined linear filter can reduce the max noise by up to 61%and the mean noise by up to 67%

the proactive approach with the LMS adaptive filter can reduce the max noise by up to 79% and the mean noise by up to 87%

Page 16: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Latency Overhead ComparisonLatency Overhead Comparison

The system latency for one time resonance noise violation is simulated such that one time reboot is required in the baseline case

The latency overhead includes time of potential reboot time of clock frequency switches to avoid resonance noise and to increase clock frequency when the

resonance is gone time loss due to slowing down the clock

Latency overhead is normalized with respect to the ideal latencies for the baseline, retroactive and proactive cases.

Compared with the latency overhead of the baseline model, the retroactive method reduces it by up to 35% the proactive model with the predetermined linear filter reduces it by up to 74% the proactive model with the LMS adaptive filter reduces it by up to 93%.

Page 17: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Area Overhead ComparisonArea Overhead Comparison

We also compare the gate count from Cadence Encounter RTL Compiler The gate count overhead is only around 0.05%-0.4%

The actuator based on adaptive filter requires about 2-4X more gates to implement than that based on the predetermined filter

Page 18: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Impact of the Number of SensorsImpact of the Number of Sensors

The noise reduction is almost the same when the number of current sensors is greater than 5%of the total number of system ports, which translates to 10 − 100 current sensors for a leading chip.

This suggests that there is no need to place many sensors for the measurement.

Page 19: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

ConclusionsConclusions

We develop a novel stochastic method to predict the future current load based on the knowledge of existing current profile.

A proactive frequency actuator is proposed to suppress resonance noise on-chip programmable PLL dynamic power supply current sensors

We develop an efficient controlling algorithm to judiciously select the runtime clock frequency so that the resonance noise is contained below the tolerance bound The impact on chip performance is minimum

Compared with baseline design without frequency actuator, experimental results show that significant resonance noise reduction can be achieved.

Page 20: Stochastic Current Prediction Enabled Frequency Actuator for Runtime Resonance Noise Reduction

Thank you!