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Date:   Wed, 17 May 2023 09:07:56 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        "H . Peter Anvin" <hpa@zytor.com>, Paul Turner <pjt@google.com>,
        linux-api@vger.kernel.org, Christian Brauner <brauner@kernel.org>,
        Florian Weimer <fw@deneb.enyo.de>, David.Laight@ACULAB.COM,
        carlos@redhat.com, Peter Oskolkov <posk@posk.io>,
        Alexander Mikhalitsyn <alexander@mihalicyn.com>,
        Chris Kennelly <ckennelly@google.com>,
        Ingo Molnar <mingo@redhat.com>,
        Darren Hart <dvhart@infradead.org>,
        =?utf-8?B?QW5kcsOvwr/CvQ==?= Almeida <andrealmeid@igalia.com>,
        libc-alpha@sourceware.org, Steven Rostedt <rostedt@goodmis.org>,
        Jonathan Corbet <corbet@lwn.net>, longman@redhat.com
Subject: Re: [RFC PATCH 0/4] Extend rseq with sched_state field
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References: <20230517152654.7193-1-mathieu.desnoyers@efficios.com>
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+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 Andr=E9 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
>