[Nook HD, HD+ Android Development] amaces:
All Things Kernel

The information below (branch names, kernel progress, etc) is slowly becoming out of date (post #2 in the Marshmallow thread has more details). Although it feels pretty archaic at this point, I'm leaving this information here, mostly for historical reasons.

My primary focus has been and continues to be an even better kernel. Instead of opening a separate thread, I will be using this space for kernel updates and related information, in a sort of log format.

Since making any of the fancier OMAP-specific kernel trees work properly is a huge headache with limited benefits, I just merged the linux-3.0.101 patches, mainly for testing (the d-3.0 branch). These patches may help with the ARM core, not so much with OMAP parts, and certainly no change to any of the Nook-specific systems. Subjectively, the normal kernel still feels marginally more stable, but hey, everything still works.

It's mid May, and for the past couple of weeks, branch g-3.0 has slowly become my default kernel. It contains additional merges from the Google 3.0 OMAP kernel, the .101 commits, plus cherry-picked changes from various sources. Hopefully, all these make for a better kernel, although the holy grail remains K3.4…

I've been experimenting with improvements upon KSM; UKSM and PKSM are supposed to better recover duplicated/lost RAM (the former in the default g-3.0 branch, the latter in p-3.0). As with KSM, they need to be enabled (and optimally tuned) through the sysfs interface (echo 1 > /sys/kernel/mm/[up]ksm/run).

A significant number of patches were added for LZ4 support, and to make zram/zcache actually use it. I think it makes things snappier, but we'll have to wait and see. Also, it turns out that good old KSM is better after all; PKSM creates instability, and UKSM is a lot more CPU hungry, very much undesired on an already underpowered device.

Another exciting week for K3.0… [MENTION=4243514]Hashcode[/MENTION] uploaded a bunch of LMK/low RAM/etc optimizations for some AMZ/OMAP44xx variants, which I'm stealing for the HDs. As I'm better understanding the use of MFLAG/QOS for frame prioritization, I ported some of these changes from K3.4. The most exciting however, is the DMA-buffered K3.0 that I have working (branch dma-buf). It definitely feels better, although figuring out how to completely switch away from memory carveouts, fix the communication with OMX/Ducati for HW accelerated video, is complicated. This branch will remain an experimental project till K3.4 is up and running.

Just for testing, I'm rebasing most of my changes on top of the official CM12.1 kernel, and made the new iosched branch default for a while. This branch contains many changes to the block layer, cherry-picked from [MENTION=3332811]faux123[/MENTION]'s tuna kernel. We now have newer I/O schedulers, such as FIOPS, ROW, and eventually BFQ. The current default elevator is ROW with 256 KB readahead. A few other interesting patches popped up, mainly related to unaligned access on ARM, and related optimizations.

Since July, all changes are grouped into feature branches on top of the upstream kernel, which are finally merged into the cm-12 branch, the default for the foreseeable future. This way of doing things is easier to maintain, and makes these changes easier to read, when deciding what to keep/discard for upstream.