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PowerSnap events

PowerSnap is a form of power telemetry that records how a Windows device uses energy over an interval of time, rather than at a single moment.

When a device drains its battery faster than expected or stays active when it should be idle, you need to see how its power behavior changed over time to find the cause. PowerSnap events give you that interval-level view. This article explains how PowerSnap events behave and what their payload contains, so you can use them for power diagnostics.

How PowerSnap events fire and cover intervals

The Microsoft.Windows.SRUM.Telemetry provider emits PowerSnap events. Each event provides a snapshot of power-related state over an interval, rather than only at a single point in time.

PowerSnap events can fire on device power state transitions and from a timer while a session is active. This behavior lets power diagnostics correlate changes in battery level, component power, CPU residency, thermal state, fan activity, and app-attributed energy with the time range of a user-visible session.

The interval is typically 15 minutes for screen-on sessions, but can be shorter if a trigger occurs, such as an AC/DC transition, Energy Saver turning on or off, or the device going to sleep. For screen-off/sleep/hibernate sessions, one event fires for the entire session at the end of the session, so these sessions can be much longer than 15 minutes. Intervals under 2 minutes don't fire, and Windows appends their data to the next event.

Diagnostic and trace analysis experiences use PowerSnap data to correlate power-related state with a time interval.

PowerSnap event payload

The PowerSnap event payload can include the following groups of metrics. Not every metric is available on every system or Windows version.

Metadata

Identifies the event and describes the interval, device state, and battery state it covers.

Metric Description
EventVersion PowerSnap event payload version.
CurrentTimeStamp Timestamp when the PowerSnap event was logged.
LastLoggedEventTimeStamp Timestamp of the previous logged PowerSnap event.
IntervalStartTimeStamp Timestamp when the PowerSnap interval began.
IgnoredEventsCount Number of short intervals that were skipped and merged into this event.
IntervalDurationInSeconds Length of the PowerSnap interval, in seconds.
IsMonitorOn Whether the monitor was on for the interval.
IsDC Whether the system was running on battery power.
IsEnergySaverOn Whether Energy Saver was active.
SessionType Power session type associated with the interval.
ExternalDisplayCount Number of connected external displays.
PreviousBatteryPerMyriad Battery charge at the start of the interval, in per-myriad (per 10,000) units.
CurrentBatteryPerMyriad Battery charge at the end of the interval, in per-myriad units.
PreviousBatteryRemainingCapacitymWh Remaining battery capacity at the start of the interval, in milliwatt-hours.
CurrentBatteryRemainingCapacitymWh Remaining battery capacity at the end of the interval, in milliwatt-hours.
PreviousMaxBatteryCapacitymWh Maximum battery capacity reported at the start of the interval, in milliwatt-hours.
CurrentMaxBatteryCapacitymWh Maximum battery capacity reported at the end of the interval, in milliwatt-hours.
BatteryDesignCapacitymWh Battery design capacity, in milliwatt-hours.
CurrentInstantaneousPowerMode Instantaneous power mode recorded for the interval.
PowerModeChangedInSession Whether the effective power mode changed during the containing session.
LastScreenOnSessionGuid Identifier for the related screen-on session.

Power

Reports component power draw and the number of power samples collected during the interval.

Metric Description
TotalPowerInMilliWatts Total platform battery drain power for the interval, in milliwatts.
CpuPowerInMilliWatts CPU core power for the interval, in milliwatts.
PackagePowerInMilliWatts Processor package power for the interval, in milliwatts.
GpuPowerInMilliWatts GPU power for the interval, in milliwatts.
NpuPowerInMilliWatts NPU power for the interval, in milliwatts.
EmiPowerInMilliWatts Energy Metering Interface channel power, in milliwatts per channel.
CpuPowerSamples CPU power samples collected inside the interval.
GpuPowerSamples GPU power samples collected inside the interval.
PackagePowerSamples Processor package power samples collected inside the interval.

CPU power management

Describes core cycles, idle time, and idle and concurrency residency distributions across big and little cores.

Metric Description
BigTotalCycles Processor cycles recorded on big, or high-performance, cores.
LittleTotalCycles Processor cycles recorded on little, or high-efficiency, cores.
AllTotalIdleTime Idle time recorded across all cores, in microseconds.
BigTotalIdleTime Idle time recorded for big cores, in microseconds.
LittleTotalIdleTime Idle time recorded for little cores, in microseconds.
PackageIdleAllIntervalHistogram Distribution of all-core idle interval lengths.
PackageIdleBigIntervalHistogram Distribution of big-core idle interval lengths.
PackageIdleLittleIntervalHistogram Distribution of little-core idle interval lengths.
PackageIdleAllIntervalCumulative Cumulative distribution of all-core idle interval lengths.
PackageIdleBigIntervalCumulative Cumulative distribution of big-core idle interval lengths.
PackageIdleLittleIntervalCumulative Cumulative distribution of little-core idle interval lengths.
AllCoresConcurrencyHistogram Distribution of the number of concurrently active cores.
BigCoresConcurrencyHistogram Distribution of concurrently active big cores.
LittleCoresConcurrencyHistogram Distribution of concurrently active little cores.
AllCoresConcurrencyCumulative Cumulative distribution of all-core concurrency.
BigCoresConcurrencyCumulative Cumulative distribution of big-core concurrency.
LittleCoresConcurrencyCumulative Cumulative distribution of little-core concurrency.
CStateHistogram Package C-state residency distribution.
CStateCumulative Cumulative package C-state residency distribution.

P-state histograms

Captures processor frequency (P-state) residency by quality of service (QoS) class and core type, as both interval and cumulative distributions.

Metric Description
PStatesBigHighQosHistogram Frequency residency for high-QoS work on big cores.
PStatesLittleHighQosHistogram Frequency residency for high-QoS work on little cores.
PStatesBigLowQosHistogram Frequency residency for low-QoS work on big cores.
PStatesLittleLowQosHistogram Frequency residency for low-QoS work on little cores.
PStatesBigTotalHistogram Total frequency residency for big cores.
PStatesLittleTotalHistogram Total frequency residency for little cores.
PStatesBigHighQosCumulative Cumulative high-QoS frequency residency for big cores.
PStatesLittleHighQosCumulative Cumulative high-QoS frequency residency for little cores.
PStatesBigLowQosCumulative Cumulative low-QoS frequency residency for big cores.
PStatesLittleLowQosCumulative Cumulative low-QoS frequency residency for little cores.
PStatesBigTotalCumulative Cumulative total frequency residency for big cores.
PStatesLittleTotalCumulative Cumulative total frequency residency for little cores.

Thermal

Reports time spent at each thermal signal or threshold, plus a temperature readout when available.

Metric Description
THERMAL_STATUS (Index 0) Time with a thermal status signal, in seconds.
THERMAL_PROC_HOT (Index 1) Time with processor hot asserted, in seconds.
THERMAL_CRITICAL_TEMP (Index 2) Time at a critical thermal condition, in seconds.
THERMAL_THRESHOLD_1 (Index 3) Time at thermal threshold 1, in seconds.
THERMAL_THRESHOLD_2 (Index 4) Time at thermal threshold 2, in seconds.
THERMAL_POWER_LIMITATION (Index 5) Time under thermal power limitation, in seconds.
THERMAL_READOUT (Index 6) Thermal readout in degrees Celsius, when available.

Fan

Describes fan on-time and the distribution of fan activity across noise and impact buckets.

Metric Description
FanOnTotalTimeInSeconds Total time the fan was on during the interval, in seconds.
FanImpactNoiseHistogram Distribution of fan time by fan impact or noise bucket.
FanImpactNoiseCumulative Cumulative distribution of fan impact or noise buckets.
FanImpactZonesHistogram Distribution of fan time by impact zone.
FanImpactZonesCumulative Cumulative distribution of fan impact zones.
FanRpmBucketBoundaries RPM boundaries for fan buckets.
FanImpactZonesBoundaries RPM boundaries for fan impact zones.

App power attribution (E3)

The Energy Estimation Engine (E3) attributes interval energy to apps, display, GPU, and other categories, including energy merged from skipped intervals.

Metric Description
TotalAppEnergySessionInMilliJoules Total app-attributed energy in the interval, in millijoules.
TotalAppEnergyMissedSessionsInMilliJoules App-attributed energy from skipped intervals, merged into this event, in millijoules.
TotalDisplayEnergySessionInMilliJoules Display-attributed app energy in the interval, in millijoules.
TotalDisplayEnergyMissedSessionsInMilliJoules Display-attributed app energy from skipped intervals, in millijoules.
TotalGpuEnergyInMilliJoules GPU energy attributed by E3 in the interval, in millijoules.
TotalGpuEnergyMissedSessionsInMilliJoules GPU energy from skipped intervals, in millijoules.
TotalLossEnergyInMilliJoules E3 loss energy for the interval, in millijoules.
TotalOtherEnergyInMilliJoules E3 other energy for the interval, in millijoules.
TotalUnknownAppEnergyInMilliJoules E3 energy attributed to unknown app activity, in millijoules.
UnknownAppDurationInSeconds Duration associated with unknown app energy, in seconds.
AttributedToSpecificAppInMyriad Share of app energy attributed to named apps, in per-myriad units.
AppEnergyNames App or package names for top app-attributed records.
AppEnergySessionInMilliJoules Per-app non-display energy in the interval, in millijoules.
AppEnergyMissedSessionsInMilliJoules Per-app non-display energy from skipped intervals, in millijoules.
AppDisplayEnergySessionInMilliJoules Per-app display energy in the interval, in millijoules.
AppDisplayEnergyMissedSessionsInMilliJoules Per-app display energy from skipped intervals, in millijoules.

SleepStudy reports

SleepStudy HTML reports can include PowerSnap data when PowerSnap collects events for a session. To generate a report, run powercfg /sleepstudy in a terminal. SleepStudy processes the PowerSnap payload for report readability, and the payload is only a subset of all the information PowerSnap collects.

Notes and limitations

  • Field availability varies by Windows version, device platform, processor topology, firmware, and available sensors.
  • Some fields can be empty or zero when a platform doesn't expose the corresponding hardware data.
  • App names and power attribution can reveal user or workload activity. Treat PowerSnap events and reports that contain PowerSnap data as diagnostic data.
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