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([39.170.101.209]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ed477a97bcsm1385255ad.13.2026.11.05.20.36.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 20:36:15 -0800 (PST) From: Ping Li To: james.morse@arm.com, ben.horgan@arm.com Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, reinette.chatre@intel.com, fenghuay@nvidia.com Subject: arm_mpam: selecting hard or soft MBW_MAX limits Date: Fri, 6 Nov 2026 12:36:11 +0800 Message-Id: <20261106043611.790930-1-leeonion.muyu@gmail.com> X-Mailer: git-send-email 2.34.1 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi Ben, mbw_max support in the driver always programs MPAMCFG_MBW_MAX without setting MPAMCFG_MBW_MAX.HARDLIM, so the limit is always soft: a PARTID above its MAX contends with low priority for bandwidth beyond the limit, but is not prevented from exceeding it. On our platform we would like to be able to select the hard limit, where a PARTID above its MAX is throttled even when the system is otherwise idle - soft limits let a noisy task exceed its limit and disturb higher-priority work when bandwidth contention appears. MPAMF_MBW_IDR.MAXLIM reports whether the MSC implements a hard limit, a soft limit, or both, but the driver does not read it today. Is there a preferred way to expose this choice? The options we see: - a mount option or info flag, if the choice must be global - a per-resource or per-group resctrl knob - selecting hard limits by default whenever MAXLIM reports the MSC supports them Thanks, Ping