Unnecessary offine/online CPU cores on each preference change

[Decatf]

It is not necessary to bring the CPU core offline then online each time a preference change is made. It's currently being done on governor change and min/max frequency change.

This behavior is problematic on the Galaxy Tab 10.1 a.k.a. p7510/p7500 a.k.a. p4wifi/p4. It's uses a kernel based on Linux 3.1.10 and hotplugging is completely broken for this device. Taking a cores offline and online will crash the kernel.

I think this behavior is overkill anyways. I pretty sure it's not a requirement of the cpufreq interface to hotplug the cores like this.

Here's a change that fixes the issue on my device. Decatf/android_packages_apps_DeviceControl@eafecfda7e2bb32df2824b69ec5c7c57cbd6417c

[amartinz]

This behavior is a requirement for almost every device i know.

If a core is not online, the toggles are not present and changing anything in fact does nothing on such devices. Bringing all cores online to switch the configuration is needed to make it stick on 95% of the devices (excluded are those with fixed kernel, means those which share cpu policies)

[Decatf]

It looks like it toggles the core regardless of whether it's online already. What about first checking if it is online or offline. So only bring online a core if it is offline.

This could maintain the previous behavior while also removing an unnecessary turning offline/online of already online cores. Would this work?

[amartinz]

If the core is already online, writing 1 to bring it online does not matter at all, as far as i know.

reading, checking and writing has a higher cost than just writing.

[Decatf]

It turns off the core and turns it back on in onlineCpu()

    sb.append(Utils.getWriteCommand(pathOnline, "0"));
    sb.append(Utils.getWriteCommand(pathOnline, "1"));