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=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 3F5D9C47094 for ; Thu, 10 Jun 2021 13:00:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24457613F1 for ; Thu, 10 Jun 2021 13:00:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230508AbhFJNCH (ORCPT ); Thu, 10 Jun 2021 09:02:07 -0400 Received: from foss.arm.com ([217.140.110.172]:59454 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230312AbhFJNCF (ORCPT ); Thu, 10 Jun 2021 09:02:05 -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 86B22106F; Thu, 10 Jun 2021 06:00:08 -0700 (PDT) Received: from e113632-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C09813F73D; Thu, 10 Jun 2021 06:00:05 -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 , Mark Rutland , kernel-team@android.com Subject: Re: [PATCH v9 12/20] sched: Allow task CPU affinity to be restricted on asymmetric systems In-Reply-To: <20210608180313.11502-13-will@kernel.org> References: <20210608180313.11502-1-will@kernel.org> <20210608180313.11502-13-will@kernel.org> Date: Thu, 10 Jun 2021 14:00:03 +0100 Message-ID: <875yyldgdo.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 08/06/21 19:03, 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. > > Although userspace can carefully manage the affinity masks for such > tasks, one place where it is particularly problematic is execve() > because the CPU on which the execve() is occurring may be incompatible > with the new application image. In such a situation, it is desirable to > restrict the affinity mask of the task and ensure that the new image is > entered on a compatible CPU. From userspace's point of view, this looks > the same as if the incompatible CPUs have been hotplugged off in the > task's affinity mask. Similarly, if a subsequent execve() reverts to > a compatible image, then the old affinity is restored if it is still > valid. > > In preparation for restricting the affinity mask for compat tasks on > arm64 systems without uniform support for 32-bit applications, introduce > {force,relax}_compatible_cpus_allowed_ptr(), which respectively restrict > and restore the affinity mask for a task based on the compatible CPUs. > > Reviewed-by: Quentin Perret > Signed-off-by: Will Deacon Reviewed-by: Valentin Schneider