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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 17E67C4743E for ; Fri, 4 Jun 2021 17:10:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0026761359 for ; Fri, 4 Jun 2021 17:10:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230161AbhFDRMo (ORCPT ); Fri, 4 Jun 2021 13:12:44 -0400 Received: from foss.arm.com ([217.140.110.172]:43740 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229690AbhFDRMn (ORCPT ); Fri, 4 Jun 2021 13:12:43 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D020B1063; Fri, 4 Jun 2021 10:10:56 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 11AEF3F73D; Fri, 4 Jun 2021 10:10:53 -0700 (PDT) From: Valentin Schneider To: Will Deacon , 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 , kernel-team@android.com Subject: Re: [PATCH v8 05/19] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection In-Reply-To: <20210602164719.31777-6-will@kernel.org> References: <20210602164719.31777-1-will@kernel.org> <20210602164719.31777-6-will@kernel.org> Date: Fri, 04 Jun 2021 18:10:46 +0100 Message-ID: <878s3peesp.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/06/21 17:47, Will Deacon wrote: > 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. > Nit: Some uses of this mask (cpu_is_allowed(), __set_cpus_allowed_ptr()) don't apply to kthreads. This makes sense for the 32-bit@EL0 faff, but it wouldn't hurt to point this out somewhere IMO. Also, that's an odd place for the definitions, but IIRC there isn't a much better choice. Reviewed-by: Valentin Schneider 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=-9.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 52220C4743D for ; Fri, 4 Jun 2021 17:12:49 +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 25E54613F9 for ; Fri, 4 Jun 2021 17:12:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 25E54613F9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com 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:Message-ID:Date:References :In-Reply-To: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=IZ4QY9Rvx4ifDDeCq0l+xbPdDPmwsvhsdUbo6/PZvwk=; b=HI/8uzSI/OCDxo JLxmCVkI2QFQPwQSEy0memX4wvKMsgDn65ZMoqsaJsKjOo3ER2xwDQKskH1/Pff9QIw/JA/eTXIM0 +EwTRisN2XcKHeaHfgg7nNd0XJtxeOpJYatSQPyDJo88rcWwAGfokh1t8qXzlBjbQMeGNQ0f4VFqu SRYZK+POASWdrjbtjqfjy/G617f/yS3zRBt8oKh9VZg2cQQ7vzI0qWskesrmXV2xhElGnVda0DI7N BcwM7TRr85lOm2GZJ1DNVlRebUmm2OI5Jes20TViNEFhf9O3Cs58lCV6P2eMlHK7U1+XXPQ9PcVyS 7Ikh28QTQ+xvmw8VA8kA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lpDLd-00EY68-AH; Fri, 04 Jun 2021 17:11:05 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lpDLY-00EY2i-3W for linux-arm-kernel@lists.infradead.org; Fri, 04 Jun 2021 17:11:01 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D020B1063; Fri, 4 Jun 2021 10:10:56 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 11AEF3F73D; Fri, 4 Jun 2021 10:10:53 -0700 (PDT) From: Valentin Schneider To: Will Deacon , 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 , kernel-team@android.com Subject: Re: [PATCH v8 05/19] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection In-Reply-To: <20210602164719.31777-6-will@kernel.org> References: <20210602164719.31777-1-will@kernel.org> <20210602164719.31777-6-will@kernel.org> Date: Fri, 04 Jun 2021 18:10:46 +0100 Message-ID: <878s3peesp.mognet@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210604_101100_214904_F778B0E5 X-CRM114-Status: GOOD ( 13.82 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 02/06/21 17:47, Will Deacon wrote: > 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. > Nit: Some uses of this mask (cpu_is_allowed(), __set_cpus_allowed_ptr()) don't apply to kthreads. This makes sense for the 32-bit@EL0 faff, but it wouldn't hurt to point this out somewhere IMO. Also, that's an odd place for the definitions, but IIRC there isn't a much better choice. Reviewed-by: Valentin Schneider _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel