DragonFly On-Line Manual Pages
POWERD(8) DragonFly System Manager's Manual POWERD(8)
NAME
powerd - simple CPU performance control and battery life monitor
SYNOPSIS
powerd [-cdeftQU] [-b backlight_percentage] [-h highest_freq]
[-l lowest_freq] [-p hysteresis] [-r poll_time] [-u trigger_up]
[-B minimum_battery_life] [-H lowtemp:hightemp]
[-L battery_life_linger] [-P battery_poll_interval]
[-T sample_time]
DESCRIPTION
The powerd daemon monitors the CPU load and automatically adjusts the CPU
performance up or down accordingly.
The powerd also monitors battery life. If the battery life is low (less
than or equal to 2% by default), powerd will send audio alert
immediately, and shutdown the machine after lingering for a little while
(60 seconds by default).
The options are as follows:
-b backlight_percentage
Set backlight to the specified percentage, if AC
line is not plugged in.
-c Enable mwait C-state hint adjustment, if it is
available.
-d Debug option. Causes powerd to not go to the
background and prints some debug output to stdout.
-e Enable Intel Performance and Energy Bias Hint
adjustment, if it is available.
-f Disable CPU power domain frequency adjustment. CPU
power domain frequency adjustment does not reduce
CPU power consumption much (if any) on some of the
modern Intel CPUs, when the CPU is idle.
-h highest_freq If CPU power domain frequency adjustment is enabled,
then frequency of CPU power domains will not be set
to a value higher than the specified limit (unit:
MHz).
-l lowest_freq If CPU power domain frequency adjustment is enabled,
then frequency of CPU power domains will not be set
to a value lower than the specified limit (unit:
MHz).
NOTE: This option is ignored if powerd is in
temperature management. Temperature management will
lower the frequency in excess of this value if
necessary (but usually doesn't have to).
NOTE: If you are using a serial port at 115200 baud,
it is recommended you not allow the frequency to
drop below 1500 Mhz or you might lose characters.
-p hysteresis Percent of the upper limit to subtract as an
hysteresis value to scale down to the min
performance. The default is 10 (meaning 10%).
-r poll_time Polling time in seconds. Default is 1.0. Setting
this value lower will poll for load changes faster.
For example, a workstation might want to use 0.2 or
0.4. powerd can become unstable if you make this
value too small.
-t Turbo mode. Disables switching to turbo mode as
maximum frequency completely. Switching to turbo
mode as maximum frequency is enabled by default, if
the CPU supports it.
-u trigger_up Per CPU load limit in percent to force maximum
performance. The default is 25 (meaning an
instantanious load of 0.25 on a single cpu). The
load is calculated over 3 polls. It is suggested
that this value not be made lower than around 7.
-B minimum_battery_life
If battery life is less than or equal to the
specified value, the machine will start shutting
down process. Default is 2 (2% battery life left).
-H lowtemp:hightemp If the cpu temperature goes above lowtemp, powerd
will begin ramping down the cpu frequency, reaching
the lowest possible cpu frequency when the cpu
temperature reaches hightemp. The default range is
75:85 (in degrees C), which tends to hold a laptop
to ~80C under heavy load. Generally speaking, no
machine cpu should be allowed to go above 80C even
if the cpu can handle it, it means something is
seriously wrong with your cooling system and you are
stressing the cpu and mobo if you allow it.
The default range starts at 75C. Most desktops with
reasonable cooling will not exceed this value so it
makes for a good default. Laptops can easily exceed
75C, sometimes reaching into the high 80's or even
the 90's due to poor cooling and vendors tweaking
their BIOS/fan-controls to the high side to do well
in benchmarks. If you want your laptop to last,
however, you really don't want it to get that hot.
For powerd to be able to stabilize, we recommend
that a minimum of a 10C range be used. So, for
example, 70:80, or 75:85, and so forth. The user
can change this range when starting powerd by
adjusting powerd_flags in /etc/rc.conf.
This option can cause cpu fans to oscillate, and you
may need to adjust the range if the oscillation is
annoying to you. The basic reason for this is that
small changes to the cpu frequency can have a huge
effect on system power consumption, causing the
BIOS-controlled fan to react, which in turn also
changes the temperature and causes powerd to react.
-L battery_life_linger
If battery life is less than or equal to the
configured value, shutting down the machine will be
delayed by the specified value. During the delay,
alert message will be logged to the console, and
audio alert will be alarmed. If AC line is plugged
in during this delay, shutting down process will be
cancelled. Default is 60 seconds.
-P battery_poll_interval
Poll the battery life at the specified interval. If
0 is specified, battery life monitoring will be
disabled. Default is 5 seconds.
-Q Don't alarm audio alert, if the battery life is low.
-T sample_time Total sample interval in seconds. Default is 8.0.
This effects how quickly powerd ratchets down the
performance and cpus on an idle machine. Longer
times will ratchet down more slowly. For example, a
workstation might want to use a value of 30.0.
-U Don't adjust userland scheduler's usable CPUs.
EXIT STATUS
The powerd utility will exit with a non-zero code if required sysctls are
not present. If the system is unable to report temperature, powerd will
still run, but will not be able to do any temperature-based frequency
management.
If a new instance of powerd is run from the command line, it will
automatically kill any previous instance running in the background. The
system operator does not have to manually kill or signal powerd when
restarting it, simply invoke a new copy.
EXAMPLES
The defaults work well for servers but a workstation user might want to
use something like the following in their /etc/rc.conf to ratchet up the
machine more quickly in response to spike loads (such as when you are
browsing).
powerd_enable="YES"
powerd_flags="-u 7 -r 0.2 -T 60"
SEE ALSO
acpi(4), perfbias(4)
HISTORY
The powerd command first appeared in DragonFly 2.7.
BUGS
I'm shocked I tell you, shocked that there might be bugs in this program!
DragonFly 6.1-DEVELOPMENT August 16, 2015 DragonFly 6.1-DEVELOPMENT