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=-20.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS 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 E1243C4338F for ; Mon, 23 Aug 2021 09:26:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA7A6613A3 for ; Mon, 23 Aug 2021 09:26:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236162AbhHWJ1e (ORCPT ); Mon, 23 Aug 2021 05:27:34 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:39046 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235926AbhHWJ1J (ORCPT ); Mon, 23 Aug 2021 05:27:09 -0400 Date: Mon, 23 Aug 2021 09:26:25 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1629710786; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=D+4lxUsAuteV08ZJ0b4ldjv7PpetS37XL4TkF+yKsw0=; b=YLHJSQY+ynXEQuy/ZYodOlXfUD8mMdI/XAA/DX9sQqw010XFUCE6TFG793Qty8MoL45mum a1aDB4rgylQlVhX46sOlKI/+eFg38XK4WKbpeRqKhfmDA1ga/7bjcvawJ+dYdADfZMEzzk C7hg3Cyi0M4ke+uD1rwJawldja1Zlp3eKVjmNWAJMRA8OJ8kkM4BJTahNjPbqB+mvdWc/Q exWXzi8ISp1cDefNBsdsEk7zLYNYkXofrVCOHXhvUcqZCwPXlNeWkMCfql7EAYajz+on4b ecsC/Hktj0XoJ9gMKXpylY/Q1J/vIWdN9MIc6WHkXOy96EGx8lB/RnlSdCX2Bg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1629710786; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=D+4lxUsAuteV08ZJ0b4ldjv7PpetS37XL4TkF+yKsw0=; b=MUims1xPhl/dXTW8ziEz3Mdyod0clP5wJzjUlGDFpyUJpRWGs4y4ASMcRttoXVd+tAs+dy OjxmXkf4uPb6HIAg== From: "tip-bot2 for Will Deacon" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Cc: Will Deacon , "Peter Zijlstra (Intel)" , Valentin Schneider , Quentin Perret , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20210730112443.23245-2-will@kernel.org> References: <20210730112443.23245-2-will@kernel.org> MIME-Version: 1.0 Message-ID: <162971078589.25758.8977089326499284001.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: 9ae606bc74dd0e58d4de894e3c5cbb9d45599267 Gitweb: https://git.kernel.org/tip/9ae606bc74dd0e58d4de894e3c5cbb9d45599267 Author: Will Deacon AuthorDate: Fri, 30 Jul 2021 12:24:28 +01:00 Committer: Peter Zijlstra CommitterDate: Fri, 20 Aug 2021 12:32:58 +02:00 sched: Introduce task_cpu_possible_mask() to limit fallback rq selection 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. Signed-off-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Quentin Perret Link: https://lore.kernel.org/r/20210730112443.23245-2-will@kernel.org --- 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 03dee12..b9b970f 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 7fa6ce7..6f31267 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2173,7 +2173,7 @@ 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)) @@ -3124,9 +3124,7 @@ 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; } } @@ -3156,10 +3154,9 @@ 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;