Re: [RFC PATCH 0/4] Extend rseq with sched_state field

[Davidlohr Bueso]

+Cc Waiman.

On Wed, 17 May 2023, Mathieu Desnoyers wrote:

> 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