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 X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C4EFC169C4 for ; Thu, 31 Jan 2019 18:24:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D984320B1F for ; Thu, 31 Jan 2019 18:24:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728395AbfAaSYL (ORCPT ); Thu, 31 Jan 2019 13:24:11 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:49402 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726455AbfAaSYI (ORCPT ); Thu, 31 Jan 2019 13:24:08 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B6F4A1596; Thu, 31 Jan 2019 10:24:07 -0800 (PST) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 3DB393F59C; Thu, 31 Jan 2019 10:24:06 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Jonathan Corbet , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Julien Thierry , linux-doc@vger.kernel.org Subject: [RFC PATCH 3/3] sched/Documentation: Point out use of preempt_schedule_irq() Date: Thu, 31 Jan 2019 18:23:39 +0000 Message-Id: <20190131182339.9835-4-valentin.schneider@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190131182339.9835-1-valentin.schneider@arm.com> References: <20190131182339.9835-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since there are a few archs out there that call preempt_schedule_irq() within a need_resched() loop, point out that it's not needed. Signed-off-by: Valentin Schneider Cc: Jonathan Corbet Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Julien Thierry Cc: linux-doc@vger.kernel.org --- Documentation/scheduler/sched-arch.txt | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/Documentation/scheduler/sched-arch.txt b/Documentation/scheduler/sched-arch.txt index a2f27bbf2cba..ae41a94da700 100644 --- a/Documentation/scheduler/sched-arch.txt +++ b/Documentation/scheduler/sched-arch.txt @@ -59,6 +59,16 @@ Your cpu_idle routines need to obey the following rules: arch/x86/kernel/process.c has examples of both polling and sleeping idle functions. +Kernel preemption +================= +When returning from interrupt context, you should call either of +preempt_schedule() or preempt_schedule_irq() if preemption is enabled +and need_resched() is true. + +Note that, unlike preempt_schedule(), preempt_schedule_irq() handles the +enabling and disabling of IRQs. Since it also loops on need_resched(), +you don't need to have that loop in your arch code. See +arch/arm64/kernel/entry.S for an example. Possible arch/ problems ======================= -- 2.20.1