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Subject[RFC PATCH 0/4] Extend rseq with sched_state field
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This prototype extends struct rseq with a new sched_state field, which
contains a "on-cpu" flag kept up-to-date by the scheduler.

It is meant to be used by userspace adaptative mutexes to decide between
busy-wait and futex wait system call (releasing the CPU) behaviors based
on the current state of the mutex owner.

The goal is to improve use-cases where the duration of the critical
sections for a given lock follows a multi-modal distribution, preventing
statistical guesses from doing a good job at choosing between busy-wait
and futex wait behavior.

This is in response to the LWN coverage of 2023 Open Source Summit North
America (https://lwn.net/Articles/931789/) unscheduled slot "Adaptive
spinning in user space" presented by André Almeida.

Feedback is welcome!

Mathieu

Mathieu Desnoyers (4):
rseq: Add sched_state field to struct rseq
selftests/rseq: Add sched_state rseq field and getter
selftests/rseq: Implement sched state test program
selftests/rseq: Implement rseq_mutex test program

include/linux/sched.h | 12 ++
include/uapi/linux/rseq.h | 17 +++
kernel/rseq.c | 14 ++
tools/testing/selftests/rseq/.gitignore | 2 +
tools/testing/selftests/rseq/Makefile | 3 +-
tools/testing/selftests/rseq/rseq-abi.h | 17 +++
tools/testing/selftests/rseq/rseq.h | 5 +
tools/testing/selftests/rseq/rseq_mutex.c | 120 ++++++++++++++++++
.../testing/selftests/rseq/sched_state_test.c | 71 +++++++++++
9 files changed, 260 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/rseq/rseq_mutex.c
create mode 100644 tools/testing/selftests/rseq/sched_state_test.c

--
2.25.1

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