Message ID | 20230529191416.53955-1-mathieu.desnoyers@efficios.com |
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Return-Path: <libc-alpha-bounces+patchwork=sourceware.org@sourceware.org> X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 55E5D385660D for <patchwork@sourceware.org>; Mon, 29 May 2023 19:14:47 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 55E5D385660D DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1685387687; bh=sPINeHvJX5lYryNeMvChlUTHeLgySd6hV/PHqz10wv0=; h=To:Cc:Subject:Date:List-Id:List-Unsubscribe:List-Archive: List-Post:List-Help:List-Subscribe:From:Reply-To:From; b=RDZ6OFCcMfDhneiNevNItvN/e1uRhJXmkVtjojjnOAyQjVNyu00/elRIsDYDeEpH0 eptDLIkwSvzLE7Yuk4o8ly4slL1LoJvyvbGQDp8qtCQ0/Hs7l73QnaclpgLqHr95kc HaB91bZRm8uGquMMkb7sWEbxN10CLzt2Ru2q7BEA= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) by sourceware.org (Postfix) with ESMTPS id A6C063858C31 for <libc-alpha@sourceware.org>; Mon, 29 May 2023 19:14:23 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org A6C063858C31 Received: from localhost.localdomain (192-222-143-198.qc.cable.ebox.net [192.222.143.198]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4QVQF94MPDz16DG; Mon, 29 May 2023 15:14:21 -0400 (EDT) To: Peter Zijlstra <peterz@infradead.org> Cc: 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>, Davidlohr Bueso <dave@stgolabs.net>, =?utf-8?q?Andr=C3=A9_Almeida?= <andrealmeid@igalia.com>, libc-alpha@sourceware.org, Steven Rostedt <rostedt@goodmis.org>, Jonathan Corbet <corbet@lwn.net>, Noah Goldstein <goldstein.w.n@gmail.com>, Daniel Colascione <dancol@google.com>, longman@redhat.com, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Subject: [RFC PATCH v2 0/4] Extend rseq with sched_state_ptr field Date: Mon, 29 May 2023 15:14:12 -0400 Message-Id: <20230529191416.53955-1-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-5.8 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_SHORT, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list <libc-alpha.sourceware.org> List-Unsubscribe: <https://sourceware.org/mailman/options/libc-alpha>, <mailto:libc-alpha-request@sourceware.org?subject=unsubscribe> List-Archive: <https://sourceware.org/pipermail/libc-alpha/> List-Post: <mailto:libc-alpha@sourceware.org> List-Help: <mailto:libc-alpha-request@sourceware.org?subject=help> List-Subscribe: <https://sourceware.org/mailman/listinfo/libc-alpha>, <mailto:libc-alpha-request@sourceware.org?subject=subscribe> From: Mathieu Desnoyers via Libc-alpha <libc-alpha@sourceware.org> Reply-To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" <libc-alpha-bounces+patchwork=sourceware.org@sourceware.org> |
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Extend rseq with sched_state_ptr field
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Message
Mathieu Desnoyers
May 29, 2023, 7:14 p.m. UTC
This prototype extends struct rseq with a new sched_state_ptr field, which points to a structure containing 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. New in this v2: - Introduce a "struct rseq_sched_state", which contains the on-cpu scheduler flag and a thread ID field. This eliminates false sharing on the struct rseq cache lines caused by busy-waiting. I have favored adding a "thread ID" field to struct rseq_sched_state rather than adding stores of owner pointer in addition to a compare-and-swap and store on a uint32_t for lock state to minimize the number of stores to perform on the fast-path. 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 | 16 +++ include/uapi/linux/rseq.h | 41 ++++++ kernel/rseq.c | 43 +++++++ tools/testing/selftests/rseq/.gitignore | 2 + tools/testing/selftests/rseq/Makefile | 3 +- tools/testing/selftests/rseq/rseq-abi.h | 42 ++++++ tools/testing/selftests/rseq/rseq.c | 13 ++ tools/testing/selftests/rseq/rseq.h | 5 + tools/testing/selftests/rseq/rseq_mutex.c | 120 ++++++++++++++++++ .../testing/selftests/rseq/sched_state_test.c | 72 +++++++++++ 10 files changed, 356 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/rseq/rseq_mutex.c create mode 100644 tools/testing/selftests/rseq/sched_state_test.c