Hello all,
Today, I would like to talk about a very interesting tool
called Powetop. This tool is used for power consumption and power management
and it finds and diagnosis different issues with powers. Using laptops when
it’s on battery, this tool can help a lot to save battery and use laptop for
longer time. For example, when you are editing a text file, there is no need to
use wifi. And even though you are not using wifi, still it consumes power for
its Idle time. So you can minimize power consumption of wifi when you are not
using it and it’s idle.
CPU is also consuming power a lot. When CPU is idle, operation
system can put it to sleep mode to save more power. When OS commands CPU to
enter to a low power state (there are different lower states), these “lower states”
called CPU C-states and it operates
on a per core basis. All C-states (C1 to Cn) put different parts of processor
to power down. C0 means no sleep and it’s up and fully operational.
There is another term that you should know as well and it’s Package C-states or PCx. When all cores agree to enter a specific C-state, it’s called
PCx. For example, if there are 2 cores and one is at C1 and the other one is
C3, the Package C-state will be C1 (highest one).
You can install powertop tool either with yum command or by
compiling actual package. The easiest way is yum command:
yum install powertool
However, if you want to download and install the latest version
of powertool manually, do the followings:
tar -txvf
powertop-2.7.tar.gz
cd powertop-2.7.tar.gz
./configure
make
make install
To run powetool:
/usr/local/sbin/powertop
Figure 1
Powetop has different tabs. The first tab is Overview and it
shows the usage, number of event per second, category, description and power
estimate of items. When you tune applications for power consumption, the number
of wakeups per second should be less which means more system’s power. To see the power estimate column on Overview tab, make sure
there is no file under /var/cache/powertop and system has to be running on battery power only. It takes
time to calculate and measure power (in terms of Watt). "Kwork" in
Category column is a placeholder process for kernel worker threads, which
perform most of the actual processing for the kernel, especially in cases where
there are interrupts, timers, I/O, etc.
Second tab is Idle State. It shows CPU’s usage currently in the
system and also it shows the current C-state of each CPU. It also shows the
same C-state by Core and Package(PCx).
Figure 2
Third tab is Frequency Stats which is frequency of cpu in terms
of GHZ in relationship with the idle state.
Figure 3
Fourth tab is Device Stats tab. It shows devices that consume
power. Figure 4.
Figure 4
Fifth tab is Tunables
tab, which is my favorite tab. It lists all devices that are not tuned for
power management and it’s marked as “Bad”. You can toggle it by pressing
“enter” from Bad to Good. Now, remember that when you reboot the machine, it’s
gone and system marks it as “Bad” again. If you want to save the setting
permanently, the command that you have to put it in .bashrc file is showing on the top when you toggle it. In this
case, it is:
echo ‘auto’ > /sys/bus/pci/devices/0000:00:15.0/power/control
Figure 5
so, do this:
cd ~
vi .bashrc
echo ‘auto’ >
/sys/bus/pci/devices/0000:00:15.0/power/control
save it.
Now, when you run powertop without any options, it goes to
interactive mode. You can store the report on html or csv file format:
powertop --html=mypowertop.html
or
powertop --csv=mypowertop.csv
Also, you can let it run for some amount of seconds:
powertop --html=mypowertop.html --time=10
Figure 6
Hope you enjoyed.
Khosro Taraghi
