Google Nexus 6 kernel

Android programmer and Kernel hacker Francisco Franco has shared on his Google+ page that the device now runs on full quad-core mode all the time. This change has resulted to a faster and smooth operation of the Google Nexus 6 on Android 5.1. This is apart from the various Framework optimizations, code being cleaned, and the several ART improvements. This also means the unit will no longer ‘hang’ because according to Franco, the Kernel task scheduler now distributes workload through all the cores.

Google seems to have disallowed built-in thread migration boost routine too–the driver developed by Qualcomm that receives notifier from the task scheduler. This happens when a thread is migrated from one cpu core to another as described by Franco. The usual lag that is experienced has been improved. The Android-Kernel programmer explained it this way:

1 – thread moves from cpu0 to cpu2
2 – driver is notified
3 – reads the current cpu0 frequency
4 – if cpu2 current frequency is less than cpu0’s read frequency it boosts cpu2 to that freq, or, if the origin freq is lower than the threshold (which is 1.7GHz by default AFAIK) it boosts to that threshold value.
5 – the boosted frequency on cpu2 stays there for at least 20ms

What he did on his FK updater was disable migrations to conserve battery life. You see, the migrations can happen a lot of times per second. Obviously, such frequent migrations can cause battery life to suffer. There really is no need for dozens of migrations so Google disabled it as noted by Franco. The results for all these changes include improved battery life and speedier performance.

No mention on other changes on the Kernel but at least we know Google is still looking on the matter.

SOURCE: Francisco Franco

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