Description¶

The Energy driver exposes the energy counters that arereported via the Running Average Power Limit (RAPL)Model-specific Registers (MSRs) via the hardware monitor(HWMON) sysfs interface.

1. Power, Energy and Time UnitsMSR_RAPL_POWER_UNIT/ C001_0299:shared with all cores in the socket
2. Energy consumed by each CoreMSR_CORE_ENERGY_STATUS/ C001_029A:32-bitRO, Accumulator, core-level power reporting
3. Energy consumed by SocketMSR_PACKAGE_ENERGY_STATUS/ C001_029B:32-bitRO, Accumulator, socket-level power reporting,shared with all cores in socket

These registers are updated every 1ms and cleared onreset of the system.

Note: If SMT is enabled, Linux enumerates all threads as cpus.Since, the energy status registers are accessed at core level,reading those registers from the sibling threads would resultin duplicate values. Hence, energy counter entries are notpopulated for the siblings.

Energy Caluclation¶

Energy information (in Joules) is based on the multiplier,1/2^ESU; where ESU is an unsigned integer read fromMSR_RAPL_POWER_UNIT register. Default value is 10000b,indicating energy status unit is 15.3 micro-Joules increment.

Reported values are scaled as per the formula

scaled value = ((1/2^ESU) * (Raw value) * 1000000UL) in uJoules

Users calculate power for a given domain by calculating

dEnergy/dTime for that domain.

Energy accumulation¶

Current, Socket energy status register is 32bit, assuming a 240W2P system, the register would wrap around in

2^32*15.3 e-6/240 * 2 = 547.60833024 secs to wrap(~9 mins)

The Core energy register may wrap around after several days.

To improve the wrap around time, a kernel thread is implementedto accumulate the socket energy counters and one core energy counterper run to a respective 64-bit counter. The kernel thread startsrunning during probe, wakes up every 100secs and stops runningwhen driver is removed.

A socket and core energy read would return the current registervalue added to the respective energy accumulator.

Sysfs attributes¶

• For index N between [1] and [nr_cpus]

• For N between [nr_cpus] and [nr_cpus + nr_socks]