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=-6.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 45A47C433EF for ; Fri, 17 Sep 2021 16:58:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31008611C4 for ; Fri, 17 Sep 2021 16:58:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245163AbhIQQ73 (ORCPT ); Fri, 17 Sep 2021 12:59:29 -0400 Received: from foss.arm.com ([217.140.110.172]:55516 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244962AbhIQQ7P (ORCPT ); Fri, 17 Sep 2021 12:59:15 -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 48391101E; Fri, 17 Sep 2021 09:57:53 -0700 (PDT) Received: from [192.168.0.14] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E356C3F59C; Fri, 17 Sep 2021 09:57:50 -0700 (PDT) From: James Morse Subject: Re: [PATCH v1 09/20] x86/resctrl: Abstract and use supports_mba_mbps() To: Reinette Chatre , x86@kernel.org, linux-kernel@vger.kernel.org Cc: Fenghua Yu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , Babu Moger , shameerali.kolothum.thodi@huawei.com, Jamie Iles , D Scott Phillips OS , lcherian@marvell.com, bobo.shaobowang@huawei.com References: <20210729223610.29373-1-james.morse@arm.com> <20210729223610.29373-10-james.morse@arm.com> Message-ID: <68dc7be2-9d07-15ca-1c53-d74e17e83ba6@arm.com> Date: Fri, 17 Sep 2021 17:57:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Reinette, On 01/09/2021 22:27, Reinette Chatre wrote: > On 7/29/2021 3:35 PM, James Morse wrote: >> To determine whether the mba_mbps option to resctrl should be supported, > > mba_mbps -> mba_MBps > >> resctrl tests the boot cpus' x86_vendor. > > CPU > >> >> This isn't portable, and needs abstracting behind a helper so this check >> can be part of the filesystem code that moves to /fs/. >> Re-use the tests set_mba_sc() does to determine if the mba_sc is supported >> on this system. An 'alloc_capable' test is added so that this property >> isn't implied by 'linear'. > Why can linear not imply alloc_capable? It is a property of a MBA resource so if it is set > then it has to be a MBA resource. mba_sc depends on controls and monitors. It checks for monitors with is_mbm_enabled(), and assumes that the delay_linear property being true means the control feature must exist. I think this is fragile. For MPAM, delay_linear is always true. Any way of controlling the bandwidth has this property. Its very likely to be set statically in the struct, regardless of whether the controls exist. alloc_capable seems to mean 'controls exist'. This is to avoid an annoying bug where supports_mba_mbps() reports true, but the controls aren't available. Or equally annoying, for the arch code to set/clear that flag in addition to alloc_capable. I'll add some verbage about MPAM to the commit message. Thanks, James