From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4161BC7EE23 for ; Wed, 17 May 2023 15:27:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232405AbjEQP1g (ORCPT ); Wed, 17 May 2023 11:27:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232353AbjEQP1U (ORCPT ); Wed, 17 May 2023 11:27:20 -0400 Received: from smtpout.efficios.com (unknown [IPv6:2607:5300:203:b2ee::31e5]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EBC58A24A; Wed, 17 May 2023 08:27:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1684337223; bh=dIw3rhHMZ7Lp2h8DWiNDF2A2BTJ7aMsSgYnH7zjBLU8=; h=From:To:Cc:Subject:Date:From; b=Ma0LIvxE0jZ5ZvZwg6GwgWj+R1P3SB+GJKRMi9UulYmtLrksnVnQkJ9z/UK54Bzno kQjEoMfbNmFmXiz0lN0ihUTjEDPpiZUwRWbnB8aJDrk1U12zEil19+/Rdy6YSBQzoF TQ/O0+hPRr4KZZz3icQDL6t+VJHP7PKMKO+n/uvHHNe6xdVWNAbLco6aXWwuzpTaJh ciAkvV1+RT7sfGvMIEHxbEglHeziORNeGVcjS6pBMsdY/x39g96eoTXxE1uX3wFxH0 97O7NlHgZJ6S/F2I7GK60igTX+RcJsj5r5URFbyrVT4L8kvK9WOmB9U9QHIC2MlpSU uinfMzhVaNCvQ== Received: from localhost.localdomain (192-222-143-198.qc.cable.ebox.net [192.222.143.198]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4QLxmR1RqKz131q; Wed, 17 May 2023 11:27:03 -0400 (EDT) From: Mathieu Desnoyers To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , "Paul E . McKenney" , Boqun Feng , "H . Peter Anvin" , Paul Turner , linux-api@vger.kernel.org, Christian Brauner , Florian Weimer , David.Laight@ACULAB.COM, carlos@redhat.com, Peter Oskolkov , Alexander Mikhalitsyn , Chris Kennelly , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?UTF-8?q?Andr=C3=A9=20Almeida?= , libc-alpha@sourceware.org, Steven Rostedt , Jonathan Corbet , Mathieu Desnoyers Subject: [RFC PATCH 0/4] Extend rseq with sched_state field Date: Wed, 17 May 2023 11:26:50 -0400 Message-Id: <20230517152654.7193-1-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 Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org 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