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=-17.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 94C6AC4361B for ; Tue, 8 Dec 2020 13:30:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6A75923AAA for ; Tue, 8 Dec 2020 13:30:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729417AbgLHNaK (ORCPT ); Tue, 8 Dec 2020 08:30:10 -0500 Received: from mail.kernel.org ([198.145.29.99]:48590 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728786AbgLHNaK (ORCPT ); Tue, 8 Dec 2020 08:30:10 -0500 From: Will Deacon Authentication-Results: mail.kernel.org; dkim=permerror (bad message/signature format) To: linux-arm-kernel@lists.infradead.org Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Will Deacon , Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Peter Zijlstra , Morten Rasmussen , Qais Yousef , Suren Baghdasaryan , Quentin Perret , Tejun Heo , Li Zefan , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , kernel-team@android.com Subject: [PATCH v5 06/15] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Date: Tue, 8 Dec 2020 13:28:26 +0000 Message-Id: <20201208132835.6151-7-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20201208132835.6151-1-will@kernel.org> References: <20201208132835.6151-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Asymmetric systems may not offer the same level of userspace ISA support across all CPUs, meaning that some applications cannot be executed by some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do not feature support for 32-bit applications on both clusters. On such a system, we must take care not to migrate a task to an unsupported CPU when forcefully moving tasks in select_fallback_rq() in response to a CPU hot-unplug operation. Introduce a task_cpu_possible_mask() hook which, given a task argument, allows an architecture to return a cpumask of CPUs that are capable of executing that task. The default implementation returns the cpu_possible_mask, since sane machines do not suffer from per-cpu ISA limitations that affect scheduling. The new mask is used when selecting the fallback runqueue as a last resort before forcing a migration to the first active CPU. Reviewed-by: Quentin Perret Signed-off-by: Will Deacon --- include/linux/mmu_context.h | 8 ++++++++ kernel/sched/core.c | 8 +++++--- 2 files changed, 13 insertions(+), 3 deletions(-) diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h index 03dee12d2b61..bc4ac3c525e6 100644 --- a/include/linux/mmu_context.h +++ b/include/linux/mmu_context.h @@ -14,4 +14,12 @@ static inline void leave_mm(int cpu) { } #endif +/* + * CPUs that are capable of running task @p. By default, we assume a sane, + * homogeneous system. Must contain at least one active CPU. + */ +#ifndef task_cpu_possible_mask +# define task_cpu_possible_mask(p) cpu_possible_mask +#endif + #endif diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e7e453492cff..58474569a2ea 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1708,7 +1708,10 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu) if (is_per_cpu_kthread(p)) return cpu_online(cpu); - return cpu_active(cpu); + if (!cpu_active(cpu)) + return false; + + return cpumask_test_cpu(cpu, task_cpu_possible_mask(p)); } /* @@ -2318,10 +2321,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p) } fallthrough; case possible: - do_set_cpus_allowed(p, cpu_possible_mask); + do_set_cpus_allowed(p, task_cpu_possible_mask(p)); state = fail; break; - case fail: BUG(); break; -- 2.29.2.576.ga3fc446d84-goog