From patchwork Tue Jun 8 18:02:58 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 12307833 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=-17.2 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 808F1C47082 for ; Tue, 8 Jun 2021 18:07:08 +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 528F261246 for ; Tue, 8 Jun 2021 18:07:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 528F261246 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@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=YJyex0o4HJysyGkdOXduYud13C96B8rHYZmEsBbKk8U=; b=scdLifRw7cy8JM Oo948JEo1fWdL69gRm6EF8LFM+X14jW2FfhY32Xc0IBOFiPIrPZbkS25s3bmnny5UkonlsR4TH9UW ETNivHPeud8THTxynIZJTv4Zhuh0iKbH1RNvDRSksVmNGmCobw9QRiVOU60O8ugv1qY78+m2lYbF0 T23DtQgkgTKZ4XjRFi/nt0OEZZ259sZ6GOZLBKD8LS49ynkyOCc4KulLyX1uo93JJiFTYe7iFVyZK zibPno30yVStNupA94GSXNa0OvI/04vkzljKTlKXKchPavMkl9iagMephvwqOv/KDXQ0LhuhzbNKf XL6sl+xwzrIXvDFs172Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lqg6M-009rXS-Gw; Tue, 08 Jun 2021 18:05:22 +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 1lqg4p-009qn8-Ns for linux-arm-kernel@lists.infradead.org; Tue, 08 Jun 2021 18:03:49 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id B5506613BC; Tue, 8 Jun 2021 18:03:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623175427; bh=LkvaF5Dq+vp9rMRP7GG2Svg0+9J+Q0X0+zzCOs62KPg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KTnCxmzrFeijhsDVs0VpqLyV7vUif59kFXGTWhjLcKqLYnBWLUryi+TrYpfb/WEQl thgB3Fkhsccc9+JGaCfjDnp/e3KcV3M/0l3Dg4buBJ7gZK46vj3oJ9td7EyQUp1Zl0 d6PyWDrYyZm/lNwE4BanCLlxNZvTTmYFGOyRQ3BLVLTITT8bDY7knWYP6ytLsslvZl wq8hvVebjEHTAtAzXCk/HOWwL34cl/MMKR5q3KH68zpTAeW/ibuX11tcFh7zxS+3zD dxcckyATEktrXGcZAEGwPbkQvHhbP0E/uCRksbg4caY8P+C1adWFSVsvGBF1CKkxu2 wa8o5pcQJ0sSw== 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 v9 05/20] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Date: Tue, 8 Jun 2021 19:02:58 +0100 Message-Id: <20210608180313.11502-6-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210608180313.11502-1-will@kernel.org> References: <20210608180313.11502-1-will@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210608_110347_850375_C7825E9D X-CRM114-Status: GOOD ( 17.05 ) 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 | 5 ++--- 2 files changed, 16 insertions(+), 3 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 5226cc26a095..0c1b6f1a6c91 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1814,7 +1814,7 @@ 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)) @@ -2792,10 +2792,9 @@ 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;