Linux – How to check what congestion algorithm supported on the linux kernel

What I want is something that checks all hardware actually supported by the kernel in use without taking into consideration if I am using that hardware or not.

If you have the .config file the kernel was built with, you can download the source and run make menuconfig, which will give you an idea of A) what hardware it is possible to configure a kernel for (but see NOTE), and B) what hardware your kernel is actually configured for.

So to do this:

1. Download the source. Your distro may have a package, or you can get them from kernel.org; find your version with uname -r.
2. Find the .config used for your kernel. If you got the source via your distro, it will hopefully be included; you may also be able to find it somewhere in /boot. Even better: often now distro kernels are built with the /proc/config.gz feature. If it exists, copy that out, ungzip it, rename the file .config and copy it into the top level of the kernel source tree.
3. Run make menuconfig from inside the top level of the source tree. You will need the ncurses development package installed (ncurses-dev or ncurses-devel) and you need to be root.

You can't do anything bad while using menuconfig beyond change the contents of the .config file, which won't matter (just don't confuse yourself with it later).

NOTE: You can't actually see all the possible hardware configurations at the same time, since different options may appear in one place based on what has been selected some other place. Kernel configuration is a bit of a labyrinth. However, you will definitely see everything that is actually selected (M means it is a module, * means it is built in).

Whether a kernel is preemptive or not depends on what you want to preempt, as in the Linux kernel, there are various things that can have preemption enabled/disabled separately.

If your kernel has CONFIG_IKCONFIG and CONFIG_IKCONFIG_PROC enabled, you can find out your preemption configuration through /proc/config.gz (if you don't have this, some distributions ship the kernel config in /boot instead):

$ gzip -cd /proc/config.gz | grep PREEMPT
CONFIG_TREE_PREEMPT_RCU=y
CONFIG_PREEMPT_RCU=y
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
# CONFIG_PREEMPT_VOLUNTARY is not set
CONFIG_PREEMPT=y
CONFIG_PREEMPT_COUNT=y
# CONFIG_DEBUG_PREEMPT is not set
# CONFIG_PREEMPT_TRACER is not set

If you have CONFIG_IKCONFIG, but not CONFIG_IKCONFIG_PROC, you can still get it out of the kernel image with extract-ikconfig.