Update docs on kernel CONFIG options used by the schedulers

[AdelKS]

@multics69 Picking the discussion I started here because it probably makes more sense to be here

If the workload heavily relies on futex

I assume futex_waitv is part of it ? how about ntsync ?

Also, are the needed kernel config options up-to-date somewhere ? I know of this file https://github.com/sched-ext/scx/blob/main/kernel.config

here's a snippet

# Bpftrace headers (for additional debug info)
CONFIG_BPF=y
CONFIG_BPF_SYSCALL=y
CONFIG_BPF_JIT=y
CONFIG_HAVE_EBPF_JIT=y
CONFIG_BPF_EVENTS=y
CONFIG_FTRACE_SYSCALLS=y
CONFIG_FUNCTION_TRACER=y
CONFIG_HAVE_DYNAMIC_FTRACE=y
CONFIG_DYNAMIC_FTRACE=y
CONFIG_HAVE_KPROBES=y
CONFIG_KPROBES=y
CONFIG_KPROBE_EVENTS=y
CONFIG_ARCH_SUPPORTS_UPROBES=y
CONFIG_UPROBES=y
CONFIG_UPROBE_EVENTS=y
CONFIG_DEBUG_FS=y
# more bpftrace to make that work
CONFIG_IKHEADERS=y
CONFIG_IKCONFIG_PROC=y
CONFIG_IKCONFIG=y

but it doesn't seem to be up-to-date, at least in the comments: I suggest that config options that aren't actually for debugging only should be moved up in that file so we know they are used outside of debugging.

Are there other config options that are actually required ? The full list that is under FTRACE is here https://github.com/gregkh/linux/blob/master/kernel/trace/Kconfig

[multics69]

I assume futex_waitv is part of it ? how about ntsync ?

Yes, futex_waitv is a part of futex implementation. LAVD tracks futex to give an additional time slice for futex holder (i.e., avoiding lock holder preemption) for better system-wide progress.

Tracing ntsync to prevent the lock holder preemption problem is on my TODO list. :-)

Also, are the needed kernel config options up-to-date somewhere ? I know of this file https://github.com/sched-ext/scx/blob/main/kernel.config

here's a snippet

# Bpftrace headers (for additional debug info)
CONFIG_BPF=y
CONFIG_BPF_SYSCALL=y
CONFIG_BPF_JIT=y
CONFIG_HAVE_EBPF_JIT=y
CONFIG_BPF_EVENTS=y
CONFIG_FTRACE_SYSCALLS=y
CONFIG_FUNCTION_TRACER=y
CONFIG_HAVE_DYNAMIC_FTRACE=y
CONFIG_DYNAMIC_FTRACE=y
CONFIG_HAVE_KPROBES=y
CONFIG_KPROBES=y
CONFIG_KPROBE_EVENTS=y
CONFIG_ARCH_SUPPORTS_UPROBES=y
CONFIG_UPROBES=y
CONFIG_UPROBE_EVENTS=y
CONFIG_DEBUG_FS=y
# more bpftrace to make that work
CONFIG_IKHEADERS=y
CONFIG_IKCONFIG_PROC=y
CONFIG_IKCONFIG=y

but it doesn't seem to be up-to-date, at least in the comments: I suggest that config options that aren't actually for debugging only should be moved up in that file so we know they are used outside of debugging.

Are there other config options that are actually required ? The full list that is under FTRACE is here https://github.com/gregkh/linux/blob/master/kernel/trace/Kconfig

LAVD first tries to use ftrace to trace futex function calls. If that is not available, it tries to use a tracepoint. (ftrace has lowe overhead than tracepoint). More specifically, it uses CONFIG_FUNCTION_TRACER.

[AdelKS]

Thanks for your input!

If that is not available, it tries to use a tracepoint

What's the kernel config option for that ? So LAVD requires either CONFIG_FUNCTION_TRACER or that, is that correct ?

Tracing ntsync to prevent the lock holder preemption problem is on my TODO list. :-)

Hehe nice!

[AdelKS]

Alright l added your info on #2969, anything else should be added ? other schedulers use other kernel config options ?