linux-kernel - [RFC PATCH 0/4] Extend rseq with sched

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Date:   Wed, 17 May 2023 11:26:50 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org, Christian Brauner <brauner@...nel.org>,
        Florian Weimer <fw@...eb.enyo.de>, David.Laight@...LAB.COM,
        carlos@...hat.com, Peter Oskolkov <posk@...k.io>,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        Chris Kennelly <ckennelly@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        André Almeida <andrealmeid@...lia.com>,
        libc-alpha@...rceware.org, Steven Rostedt <rostedt@...dmis.org>,
        Jonathan Corbet <corbet@....net>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [RFC PATCH 0/4] Extend rseq with sched_state field

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