ACPI CPUfreq vs. Intel P-State Scaling With Linux 3.15

[samdraz]

for best results use https://github.com/01org/thermal_daemon thermal daemon along with p-state

[Ericg]

using the powersave governor is not enough- you need to use something like tlp to automatically force a low max cpu frequency to maximize it's effects.

Using powersave AT ALL isn't enough, if you're actually trying to save power. Tasks will take longer to complete. The ONE use I've found for powersave is for thermalcapping when my laptop's CPU fan wasn't working. Using default P-State would make the laptop overheat under load, but using powersave let it run and run albeit slower.

Btw, every time i try to make a custom kernel with pstates, it crashes(as in, kernel panic so deep that i have to pull the battery) as soon as i pull the power cable- it does not like to be told what to do,apparently, so i stick with acpi.

Read the panic and see if it tells you if something is missing. P-States might depend on another config option. All I can tell ya is they work perfectly fine on Fedora and Arch for me. (You could have also found a CPU-specific bug, but its a little less likely haha)

[GreatEmerald]

Yea, the results make no sense. Why is pstate performance sometimes slower and using less power than pstate powersave?

[liam]

This makes no sense, Michael.

The ACPI performance governor cannot be slower than ondemand one. It just cannot - it keeps the CPU at its highest frequency all the time.

Are you sure? My understanding of the performance governor was that it only had two states: max freq(turbo?) and idle (not sure which idle states... S0i1?). Perhaps the problem is that it is to aggressive going to idle and the resulting transition times, for this hardware, are causing performance hits?

[liam]

Great article Michael! Best I've seen in awhile.
Would do mind attaching that wattmeter to the Nvidia board so we can get some official power numbers?

[Michael]

Would do mind attaching that wattmeter to the Nvidia board so we can get some official power numbers?

Thanks. Yes I do plan to, albeit I only have one WattsUp meter and am constantly using it on many different systems so unfortunately it takes a while. I hope to have the power numbers for the Jetson TK1 out next week.

[rikkinho]

intel pstate

Thanks. Yes I do plan to, albeit I only have one WattsUp meter and am constantly using it on many different systems so unfortunately it takes a while. I hope to have the power numbers for the Jetson TK1 out next week.

intel pstate is bad, really bad with battery life is bad with temps in idle and performance state dont works well

[liam]

Thanks. Yes I do plan to, albeit I only have one WattsUp meter and am constantly using it on many different systems so unfortunately it takes a while. I hope to have the power numbers for the Jetson TK1 out next week.

That's great. I look forward to it.

[linuxforall]

Colin Ian King, kernel engineer tested P state extensively with a watts meter to find out higher consumption of pstate versus acpi cpufreq and its on his recommendation pstate was disabled for Ubuntu 14.04 https://lists.ubuntu.com/archives/ke...il/041515.html

His experience reflects mine on Arch with i7 IVB laptop. I notice higher temps and more consumption, with TLP I get 4.5 hours on Ubuntu 14.04 as opposed to 3.5 hours with Arch with latest kernel 3.14 and pstate.

[Guest]

Few remarks (please correct me if I get anything wrong):

P-state has only one governor (default) which can be tweaked by 3 settings (min,max,no_turbo) via sysfs.
P-state doesn't really change frequencies, everything is running at max frequencies with sleep-states inserted according to load.

So in workloads:

gaming - everything runs on max, cpu doesn't sleep unless it's forced to by high temperature
semi-idle - everything runs on max, cpu sleeps most of the time, when there are tasks to be taken care of it wakes up and goes to sleep
idle - cpu sleeps (apart from one core that is running scheduler and poriodic tick)

It came to me as a big surprise when in past posts about P-state there were 'performance' and 'powersave' governors.
<pre>
echo 100 > /sys/devices/system/cpu/intel_pstate/max_perf_pct
echo 26 > /sys/devices/system/cpu/intel_pstate/min_perf_pct
echo 0 > /sys/devices/system/cpu/intel_pstate/no_turbo
</pre>