CPU Sleep States Analysis

The CPU Sleep States analysis monitors system hardware sleep states and explores how software behaviors are affecting those sleep states. To consume less power, different hardware components enter sleep states when they are idle. Ideally, hardware would enter a deep sleep state and stay there for a relatively long time before actively executing a workload again.

Use CPU Sleep States analysis data to analyze processor wake-up causes (for example, when the processor transitions from a sleep state to an active state). You can also determine if your application is causing wake-ups via timers. CPU Sleep States analysis can provide the call stack of the source code that scheduled a timer that later caused a wake-up.

To reduce power consumption, you can eliminate unnecessary processor wake-ups either by eliminating or by coalescing timers wherever possible. CPU Sleep State analysis provides a timeline of wake-up activity, the causes of the wake-ups, and filters that can be used to isolate different behaviors and root causes of the wake-ups. VTune Amplifier detects the following causes of the processor wake-ups:

• Kernel Timer

• User Timer

• IPI : Inter Processor Interrupt

• IRQ : Interrupt Request

During the sleep state analysis collection, Intel® VTune™ Amplifier traces processor sleep state transitions and tries to identify the cause of each wake-up. The results show a timeline of the processor sleep states - C-states (the larger the C-state, the deeper the sleep and the greater the power saving) and wake-up activity per physical core. You can use filters to show the relevant data or zoom into periods of frequent wake-up activity to determine what might be causing the hardware to consume more power than necessary.

VTune Amplifier displays the results of CPU Sleep States analysis in the CPU Sleep States viewpoint where:

• Summary window displays valuable statistics over the collection run time, such as the top five causes of wake-ups, a histogram of the Elapsed time spent in different sleep states, and so on.

• CPU Sleep States pane displays sleep state duration per physical core.

• Wake-ups pane displays details on the causes of the processor wake-ups per core. For timer wake-ups and kernel timer wake-ups of the profiled application, the Wake-ups pane displays call stacks.

• Call Stack pane displays call stacks for wake-up objects.

• Timeline pane displays the timeline of wake-up activity and distribution of the Elapsed time spent in different sleep states per core.