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Kernel Configuration and Optimization References

Below is kernel options, that was enabled in kernels like CachyOS, Xanmod github kernels compared to NixOS linux kernel ( even xanmod variation ) by default.

Useful Links

NO_HZ: Reducing Scheduling-Clock Ticks

NO_HZ_IDLE = yes; # Enabled in xanmod git kernel.

NO_HZ_IDLE: can reduce the number of scheduling-clock interrupts, thereby improving energy efficiency and reducing OS jitter. Reducing OS jitter is important for some types of computationally intensive high-performance computing (HPC) applications and for real-time applications.

NO_HZ_FULL: Full dynticks system (Tickless)

NO_HZ_FULL = yes; # Used in CachyOS.

Adaptively try to shutdown the tick whenever possible, even when the CPU is running tasks. Typically this requires running a single task on the CPU. Chances for running tickless are maximized when the task mostly runs in userspace and has few kernel activity.

By default, without passing the boot.kernelParams, this behaves just like NO_HZ_IDLE, so we can safely use NO_HZ_FULL instead of NO_HZ_IDLE. I have are few ideas with this. More on my notes.

Optimize kernel for x86_64-v* processors

GENERIC_CPU3 = yes; for x86_64-v3 processors. GENERIC_CPU4 for x86_64-v4 and so on.

AMD cpu

We can also enable compiler optimizations for AMD generation instead.

MZEN3 = yes; # for Zen3, for example. MZEN4 for zen4 and etc.

CONFIG_FW_LOADER = Firmware loading facility

Warning

Building the firmware loading facility as a module, {M} Firmware loading facility i.e. CONFIG_FW_LOADER=M ( Like NixOS linux kernel do ), might prevent early microcode updating in most setups. Source: gentoo wiki.

I personally didn't have any issues with this enabled as .

FW_LOADER = yes;

DMABUF

Who knows why "heaps" were disabled by default.

DMABUF_HEAPS = yes;
DMABUF_HEAPS_SYSTEM = yes; # Enabled in cachyos/xanmod git configs.
DMABUF_HEAPS_CMA = yes; # Disabled in xanmod GitHub config. Enabled in CachyOS.
DMABUF_MOVE_NOTIFY = yes; # Security. Disabled in CachyOS kernel, probably because of : "due to inconsistent execution context and memory management between drivers". Enabled in xanmod GitHub config.

ZSWAP

ZSWAP_SHRINKER_DEFAULT_ON = yes; # https://cateee.net/lkddb/web-lkddb/ZSWAP_SHRINKER_DEFAULT_ON.html. Good thing overall, no? Enabled in cachyos/xanmod GitHub config.
ZSWAP_COMPRESSOR_DEFAULT_LZ4 = yes; # CachyOS and NixOS kernel use zstd instead. Xanmod GitHub use LZ4.
ZSWAP_COMPRESSOR_DEFAULT = "lz4"; # above.
ZSWAP_ZPOOL_DEFAULT_Z3FOLD = yes; # NixOS xanmod and CachyOS using zmalloc. Xanmod GitHub kernel using z3fold.
ZSWAP_ZPOOL_DEFAULT = "z3fold"; # above.
Z3FOLD = yes; # above.
ZSWAP_DEFAULT_ON = yes; # enabled in CachyOS.
ZSMALLOC_STAT = yes; # enabled in CachyOS. Monitoring and debugging stuff.

ZRAM

Note

ZRAM by default is enabled as a module which is correct because it allows changing the number of zram devices without rebooting, by deactivating zram devices and re-loading the module with new parameters.

Options below were disabled in NixOS xanmod, but xanmod GitHub and CachyOS Bore + Hardened enable them.

ZRAM_TRACK_ENTRY_ACTIME = yes;
ZRAM_MEMORY_TRACKING = yes; # Track ZRAM block status.

Enabled in xanmod GitHub. LZO instead of "zstd"

ZRAM_DEF_COMP_LZORLE = yes; #
ZRAM_DEF_COMP = "lzo-rle";

TMPFS

TMPFS_INODE64 = yes; 
TMPFS_QUOTA = yes; # QUOTA support.