Energy-Efficient Software Criteria

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Checklist for creating software applications that is energy-efficient. The checklist is operating system-agnostic except where otherwise noted.

Computational Efficiency

Loops

• Minimized the use of tight loops?
• Converted polling loops to being event driven?
• Using efficient polling loops (largest possible polling interval) when polling loops are necessary?
• Eliminated busy wait (spinning) loops, where possible? Might still be required for certain locking/synchronization tasks.

Performance Libraries/Extensions

• Utilizing instruction set extensions (such asSSE instructions, AVX, or newer) to accelerate computations?
• Utilizing Performance Libraries such as Intel® Performance Primitives or Intel® Math Kernel Library?
• Utilizing on-chip video encode/decode hardware acceleration using Intel® HD Graphics and the Intel® Media Software Development Kit (Intel® Media SDK)?

Algorithms

• Using high performance algorithms and data structures (gets the job done faster)?
• If requirements allow, can you select a less complex algorithm that is more power efficient?
• Minimized use of heavily recursive algorithms (these can be power inefficient)?

Compiler Optimization Options

• Is application optimized for speed?
• Is application optimized (profiled) for most common execution path?

Drivers

• Utilizing kernel/drivers that are idle power friendly?
• Identified drivers causing excessive interrupts?

Programming Language

• Using a programming language implementation and libraries that are idle power friendly?

Maximize Idle

Multithreading

• Taking advantage of multiple threads and cores to speed-up execution? Faster execution means more time to idle.
• Are threads balanced? Imbalanced threads may increase power consumption.

Reduce usage of High-Resolution Periodic Timers

• Using a timer rate appropriate for the application? Intervals < 15ms have low benefit on most systems and serve only to reduce idle times. Always make sure to disable periodic timer in case it is not in use.
• If application increases the timer tick rate when active, remember to reset to default timer value when idle? For Microsoft* Windows*, the default system timer resolution is 15.6ms.
• (Linux) Using timer APIs in application so that timers can be grouped (e.g. round_jiffies) or utilizing deferrable kernel timers?

Data Efficiency

• Can data be pre-fetched from optical disk and buffered, allowing disk to idle?
• Can data be pre-fetched from hard-disk and buffered, allowing disk to idle?
• Avoiding frequent reads/writes to disk?
• Can read/write requests be batched into one operation?
• Using algorithms that minimize data movement, memory (cache versus RAM), and hierarchies that keep data close to the processor?
• Identified processor resources shared between cores? Synchronize threads on different cores to work simultaneously and idle simultaneously.

Context-Aware (Power-Aware) Behavior

Handling Sleep Transitions Seamlessly

• Is application preventing/delaying system sleep or hibernate state transitions? Make sure to handle appropriate transition events.
• (Microsoft* Windows*) Are you preventing System Idle Timeouts only when necessary? Remember to reset execution state when task is complete (SetThreadExecutionState).

Respond/Adapt to System Power Events

• Responding to transition between battery and AC operation?
• Handling Low Battery event by saving work/state/checkpoint? Avoid duplicating work in case of standby.
• (Windows) Responding to PBT_APMSUSPEND within two seconds?
• Application adapting to user selected OS power policy?

Scale Behavior Based on Machine Power State

• Can resource usage be reduced when on battery power (such as avoiding background updates)?
• Is it possible switch to “low-power” algorithms on Low Battery?
• Depending on machine state, have you explored the option of letting the application inform the user to select a low(er) power profile for efficient execution?

• Utilizing context awareness toolkits such as Intel® Mobile Platform SDK, Intel® Laptop Gaming TDK, or Intel® Web 2.0 TDK?

• Can unused peripherals be shut off/disabled (e.g. Bluetooth*, 802.11) if no activity?

Testing for Energy-Efficiency

Profile system power during application runtime

• Understand the power impact of application at Idle and Running state
• Examine C-state behavior
• Examine P-state behavior
• Examine timer interrupts
• Examine interrupt statistics
• Examine disk and file access statistics

For details on the above topics and references to existing white papers and articles, please refer to the extended document, Energy-Efficient Software Guidelines. This checklist created by Intel as a general suggestion. If you have feedback, suggestions, or would like more information about power management go to http://www.intel.com/software/power/.