This is another attempt at implementing UMCG, based on discussion in https://lore.kernel.org/patchwork/cover/1433967/ Most of the "why" is covered here (some details are obsolete): https://lore.kernel.org/patchwork/cover/1433967/#1632328 At a high level, UMCG servers/workers provide the foundation for an M:N threading library, as described in the link above. In addition, servers without workers can be used as "basic" UMCG tasks if wait/wake/context-switch are the only desired operations. Joel Fernandes has also once mentioned that he had a use case for a wake+bring-the-wakee-to-the-current-CPU operation, so this is now also supported via UMCG_WF_CURRENT_CPU flag (patch 3). Patch 1: add WF_CURRENT_CPU and tweak ttwu - same as last time Patch 2: add X86_64 helpers to work atomically with userspace values Patch 3: implement UMCG kernel-side In this version of the patchset I used only userspace/TLS data, as suggested by Peter Zijlstra. With the exception of one issue (see patch 3 commit message) everything seems to be working great. This TLS-only approach makes the userspace code a bit more involved, so I'm not posting libumcg/selftests with this patchset to focus on the kernel side only. TODO: - put atomic helpers from patch 2 into their proper place (unless keeping them in kernel/sched/umcg.h is OK) - fix the wake server issue in preempt disable block (see patch 3) - implement timeout handling - imlement worker preemption - more testing - manpages, docs, and similar - attach libumbc and selftest patches Peter Oskolkov (3): sched: add WF_CURRENT_CPU and externise ttwu sched/umcg: RFC: add userspace atomic helpers sched/umcg: RFC: implement UMCG syscalls arch/x86/entry/syscalls/syscall_64.tbl | 2 + include/linux/sched.h | 6 + include/linux/syscalls.h | 4 + include/uapi/asm-generic/unistd.h | 8 +- include/uapi/linux/umcg.h | 246 +++++++++++++ init/Kconfig | 10 + kernel/exit.c | 7 + kernel/sched/Makefile | 1 + kernel/sched/core.c | 20 +- kernel/sched/fair.c | 4 + kernel/sched/sched.h | 15 +- kernel/sched/umcg.c | 481 +++++++++++++++++++++++++ kernel/sched/umcg.h | 271 ++++++++++++++ kernel/sys_ni.c | 4 + 14 files changed, 1068 insertions(+), 11 deletions(-) create mode 100644 include/uapi/linux/umcg.h create mode 100644 kernel/sched/umcg.c create mode 100644 kernel/sched/umcg.h -- 2.25.1
