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.Dd January 24, 2026
.Dt CORECSTAT 4
.Os
.Sh NAME
.Nm corecstat
.Nd device driver for Intel Core C-State and Package C-State residency counters.
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device corecstat"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
corecstat_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides support for Intel's Core C-State and Package C-State residency
counters, that are provided in Nehalem and newer Core and Xeon CPUs,
as well as in Atom CPUs of the Silvermont and newer architectures.
Core C-State residency is shown for each physical CPU core, and
Package C-State residency is shown per CPU package.
The values are exposed through the
.Dv HW_SENSORS
.Xr sysctl 3
tree.
For example:
.Bd -literal -offset indent
% sysctl hw.sensors
hw.sensors.cpu2.percent0: 0.00% (node0 core0 C3 res.)
hw.sensors.cpu2.percent1: 0.00% (node0 core0 C6 res.)
hw.sensors.cpu2.percent2: 99.42% (node0 core0 C7 res.)
hw.sensors.cpu3.percent0: 0.00% (node0 core1 C3 res.)
hw.sensors.cpu3.percent1: 0.00% (node0 core1 C6 res.)
hw.sensors.cpu3.percent2: 99.62% (node0 core1 C7 res.)
hw.sensors.cpu_node0.percent0: 14.33% (node0 PC2 residency)
hw.sensors.cpu_node0.percent1: 0.03% (node0 PC3 residency)
hw.sensors.cpu_node0.percent2: 0.00% (node0 PC6 residency)
hw.sensors.cpu_node0.percent3: 85.18% (node0 PC7 residency)
hw.sensors.cpu_node0.percent4: 0.00% (node0 PC8 residency)
hw.sensors.cpu_node0.percent5: 0.00% (node0 PC9 residency)
hw.sensors.cpu_node0.percent6: 0.00% (node0 PC10 residency)
.Ed
.Pp
These numbers are useful to understand how much, and to what extent CPU
powersaving is being used. Higher numbers designate a "deeper" powersaving
state, which will use less electricity. However "deeper" powersaving states
will also include a slower wakeup time, which can sometimes degrade
interactive performance under partial system load.
You can modify the C-State powersaving behavior on these Intel CPUs by
adjusting the
.Va machdep.mwait.CX
sysctl knobs.
.Sh SEE ALSO
.Xr systat 1 ,
.Xr sysctl 3 ,
.Xr coretemp 4 ,
.Xr corepower 4 ,
.Xr devctl 4 ,
.Xr devd 8 ,
.Xr sensorsd 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Dx 6.5 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Imre Vadász Aq Mt imre@vdsz.com .