Feature: Thread Priority (sched_setattr) & Futex Queuing Discipline

[garethodickin]

Developer Contact Info:

taekyung.kang@boeing.com

Feature request summary

* Symbols (3): sched_setattr, uk_futex_set_discipline, uk_futex_del_discipline
* Root cause: Unikraft's uksched has no thread priority field and no sched_setattr syscall,
  which prevents priority-based futex wait queue ordering.
* Fix (Part 1 - Prerequisite): Add prio field to uk_thread and implement sched_setattr syscall
* Fix (Part 2 - Futex Queuing Discipline): Add FUTEX_DISCIPLINE_FIFO and FUTEX_DISCIPLINE_PRIO
  support via uk_futex_set_discipline/uk_futex_del_discipline APIs in lib/posix-futex

Describe alternatives

Adding new futex syscall commands to set queuing discipline; avoided because it modifies the standard command set.

Related architectures

arm64

Related platforms

Xen and Qemu

Additional context

Part 1 (sched_setattr / thread priority):
  Files modified: lib/uksched/Makefile.uk, lib/uksched/include/uk/thread.h, lib/uksched/sched.c
  TODO: support setting priority of other threads by tid.
  TODO: implement sched_policy, sched_nice, and deadline parameters (runtime/deadline/period).

Part 2 (futex queuing discipline):
  Files modified: lib/posix-futex/exportsyms.uk, lib/posix-futex/futex.c
  Files added: lib/posix-futex/include/uk/posix-futex-discipline.h

Dependency: Part 2 requires Part 1 because FUTEX_DISCIPLINE_PRIO relies on
the thread priority (prio) field introduced by sched_setattr.