From patchwork Fri Jul 30 11:24:28 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 12411057 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=-17.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 EA5BBC432BE for ; Fri, 30 Jul 2021 11:27:35 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B57516101C for ; Fri, 30 Jul 2021 11:27:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org B57516101C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Za+XYNtqrx2OaDQP3YSJbBDKeWjGPP5Pxf/6PNves/Y=; b=T002nA/ELB5j0W swdUPUzmJH8kVNIH4GQ6QyBcwEa8RwKZaOoFt5kAQ8PUgLiEPvQs9NjCZW8BJwmTqEg7dLr5XTsSz ZGrUMBx4GU6WJ9leGZBefI/lN/iSz8QlzPBAT1zBCJa+YG5Iu7j8WaHDhY+mzEgyeGEkG/slxXsxU IHQdWTvMp/1SyrEJkSJH9kM2jQII82gF5G0i5AnO8nYo/QyRkZO1SDg1B/nPJMx5CjlnFKwXz4Qc+ zSOeHEX278CzdW1IKCsC+oKDLjEfaJKhy4CvVHyUmfCMAZZx8HXJgKNboS2zeoxgnkk7TeNLPf/Io pMg71x4+BJOTv1QZAKJA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1m9QdV-008HOi-Nh; Fri, 30 Jul 2021 11:25:05 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1m9QdL-008HLx-Fl for linux-arm-kernel@lists.infradead.org; Fri, 30 Jul 2021 11:24:56 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8B8EB61054; Fri, 30 Jul 2021 11:24:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1627644295; bh=cMR+kmfN+LR4V8K3b19C27mYClwkFpH+EgWdYLvABQo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HsfUg5e2IISXfWTjXPkysFNubh3ludK+aWAEQc8/gOUQbIfqlfyfNYSiaXBkAC0qP tfcZKhQa7coD2ecATLTGiLAYyOsLGzqwoqyGcCPvAAkbMcW7tKgLsOCtsaQWE2aSfn J2Q+5FBbzH3erHhvz6EMIalxK0NR+6ibob5jvwukU+gOSpfSiN3C6lclmDm1Xc+bOP 3JyHpCBxbYeOEWakm170h7e1cLsBffQDMWZQdDti1gOGUwGi6ySe3oauId4BWwnaO/ 9bZqf/Niqxsi9F6KU18HSjkXNaCAUVlUuvo/2Jj0B/W/H6YA6o5ZXTKLU8EUrxGA+K 9XMDKjVjTB0iQ== From: Will Deacon 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 , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , "Rafael J. Wysocki" , Dietmar Eggemann , Daniel Bristot de Oliveira , Valentin Schneider , Mark Rutland , kernel-team@android.com, Valentin Schneider Subject: [PATCH v11 01/16] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Date: Fri, 30 Jul 2021 12:24:28 +0100 Message-Id: <20210730112443.23245-2-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210730112443.23245-1-will@kernel.org> References: <20210730112443.23245-1-will@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210730_042455_602351_80B2076B X-CRM114-Status: GOOD ( 18.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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: Valentin Schneider Reviewed-by: Quentin Perret Signed-off-by: Will Deacon --- include/linux/mmu_context.h | 14 ++++++++++++++ kernel/sched/core.c | 9 +++------ 2 files changed, 17 insertions(+), 6 deletions(-) diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h index 03dee12d2b61..b9b970f7ab45 100644 --- a/include/linux/mmu_context.h +++ b/include/linux/mmu_context.h @@ -14,4 +14,18 @@ static inline void leave_mm(int cpu) { } #endif +/* + * CPUs that are capable of running user task @p. Must contain at least one + * active CPU. It is assumed that the kernel can run on all CPUs, so calling + * this for a kernel thread is pointless. + * + * By default, we assume a sane, homogeneous system. + */ +#ifndef task_cpu_possible_mask +# define task_cpu_possible_mask(p) cpu_possible_mask +# define task_cpu_possible(cpu, p) true +#else +# define task_cpu_possible(cpu, p) cpumask_test_cpu((cpu), task_cpu_possible_mask(p)) +#endif + #endif diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 2d9ff40f4661..84b20feb3214 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2163,7 +2163,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu) /* Non kernel threads are not allowed during either online or offline. */ if (!(p->flags & PF_KTHREAD)) - return cpu_active(cpu); + return cpu_active(cpu) && task_cpu_possible(cpu, p); /* KTHREAD_IS_PER_CPU is always allowed. */ if (kthread_is_per_cpu(p)) @@ -3114,9 +3114,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p) /* Look for allowed, online CPU in same node. */ for_each_cpu(dest_cpu, nodemask) { - if (!cpu_active(dest_cpu)) - continue; - if (cpumask_test_cpu(dest_cpu, p->cpus_ptr)) + if (is_cpu_allowed(p, dest_cpu)) return dest_cpu; } } @@ -3146,10 +3144,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p) * * More yuck to audit. */ - 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;