System-level, Unified In-band and Out-of-band Dynamic Thermal Control Dong LiVirginia Tech Rong GeMarquette University Kirk CameronVirginia Tech

Motivation Hot spots or elevated temperatures in areas of the data center are quite common Out-of-band techniques (e.g. CPU cooling fans) are less studied In-band and out-of-band techniques operate independently without cooperating with each other  Challenge 1: enforcing the same user control policy across diverse physical mechanisms  Challenge 2: in needs of a tunable controller

Temperature Characteristics of Parallel Applications

Three temperature characteristics  Sudden change and gradual change lead to actual temperature increase or decrease  Jitter lacks sustained increase or decrease following a spike Design a controller to recognize these types and respond accordingly

History-based Context-aware Temperature Control (Basic idea) Periodically profile temperature and use the historical information to predict future CPU temperature Identify the appropriate technique to perform thermal control and balance power and performance for the next interval based on the prediction

History-based Context-aware Temperature Control (Temperature Profiling and Prediction) Use a two-level window to track the changes in temperature in both long and short time periods Temperature samples The level-one temperature window to react to the “sudden” Average value to reduce jitter frontrear The level-two temperature window (FIFO) to react to the “gradual”

History-based Context-aware Temperature Control (Temperature Profiling and Prediction) We assume that temperature will change with the same rate for the next round of sampling The temperature difference (  t L1/L2 ) is then used to determine the appropriate temperature regulator response

History-based Context-aware Temperature Control (Target Mode Identification) Inputs:  Predicted temperature behavior based on the temperature profile (  t L1/L2 )  A parameter (P p ) specified by the user that indicates the aggressiveness of the temperature controller Outputs:  Fan speed  Frequency setting  The controls follow the thermal control policy (P p )

History-based Context-aware Temperature Control (Target Mode Identification) We maintain a “thermal control array” for each available thermal control technique on the system {g 1, g 2, g 3, …, g n p, …, g N } Each number represents a mode that controls temperature at a degree WeakStrong Effectiveness of controlling temperature

History-based Context-aware Temperature Control (Target Mode Identification) To coordinate multiple thermal management techniques, we fill out the arrays in a unified way {g 1, g 2, g 3, …, g n p, …, g N } WeakStrong Effectiveness of controlling temperature n p is determined by P p Filled with the most effective mode g N Filled with a subset of physically available modes evenly extracted from the full set

History-based Context-aware Temperature Control (Target Mode Identification) n p is determined by P p P MIN P MAX 1N Mapping npnp PpPp

History-based Context-aware Temperature Control (Target Mode Identification) P MIN P MAX 1N Mapping npnp PpPp {g 1,…,,…, g N }gnpgnp A smaller P p leads to a more aggressive thermal control  More array items store the most efficient temperature mode  A small increment in array index can lead to large increment in cooling effect

History-based Context-aware Temperature Control (Target Mode Identification) We use the predicted temperature variance (  t L1/L2 ) from the two-level window to identify an index in the thermal control array {g 1,…, g i,…g i+c*  t,…, g N } current modenext mode T MIN T MAX 1N Mapping C = (N-1)/(T max – T min )

Performance Evaluation (Platform) Implement a fan driver that dynamically set the fan speed according to processor temperature Collect temperature samples from digital thermal sensors embedded in the processor The processor can be scaled among 5 frequencies

Performance Evaluation (Dynamic Fan Control) Our dynamic fan control responds to temperature changes under different control policies (P p =25 (aggressive), P p =50(moderate), and P p =75(weak))

Performance Evaluation (Dynamic Fan Control) P p = 50; benchmark: bt.B.4 We compare our dynamic fan control method with the traditional static method and constant fan speed control

Performance Evaluation (Dynamic Fan Control) In general, larger maximum PWM duty cycle leads to lower temperature A less powerful fan is able to deliver similar cooling effects as a more powerful fan with our dynamic control

Performance Evaluation (Temperature Aware DVFS Control) Benchmark: LU.B.4; coupled with traditional static fan control; P p =50 Our DVFS control scales down frequency only when average temperature is stabilized Our DVFS control scales up frequency to its original value once the temperature is consistently below the threshold so as to avoid performance loss

Performance Evaluation (Temperature Aware DVFS Control) Our DVFS control performs better than CPUSPEED in terms power-saving and performance CPUSPEEDtDVFS Max allowed PWM duty cycle 75%50%25%75%50%25% # freq changes Execution Time (s) Ave Power(Watt) Power-Delay Product (Watt*s)

Performance Evaluation (Dynamic Hybrid Fan and DVFS Control) Our method effectively unifies different thermal control techniques and reacts to different user control policies with minimum performance impact

Conclusion We classify thermal characteristics of parallel applications and use a two-level temperature window to make our controller more effective We introduce a simple parameter (P p ) to allow the user to specify the aggressiveness of in-band and out- of-band techniques for thermal reductions We integrate an out-of-band method (fan control) and an in-band method (DVFS) We explore an efficient fan control method

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