From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id BB7F42F0C67 for ; Mon, 19 Jan 2026 20:56:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768856186; cv=none; b=kOYvnQPMbVtgmAZjR24cX4YdIOiMRZ2xpCdfxHNmH5ogOGb50Au2tcDkiWgEkRE0JCM7Yt1Al/WN7lCh+PBeLTPd6FWe8J1zxJn3RHx3dynPQgT65915mPkNe+4euA/eHodu72kp1iBI/y1lqggUortMTB25TJnl6MerknV5CYk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768856186; c=relaxed/simple; bh=4CH8pG7wjq6w95XCA7UD3AxRn4bcT2I7HuRscj1Rr4Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pNJ+PLb8GrH0hwjIlhDaikuxUsGvs/x86QDGUSMeJOEIOisk8VrxHktd6dktc2loSw94qfPcScYXU95C09Us6MWmcKuu7TL0UhbXeVwO2a4HlnnpA/c7q1VxO8nYHkcOAS3e2rCOEqwu3nGNO+qyeCNWpa6SGj8tJmrUWRm7//U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 8D82F497; Mon, 19 Jan 2026 12:56:17 -0800 (PST) Received: from [10.1.196.46] (e134344.arm.com [10.1.196.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 63C783F632; Mon, 19 Jan 2026 12:56:19 -0800 (PST) Message-ID: Date: Mon, 19 Jan 2026 20:56:17 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 45/47] arm_mpam: Add workaround for T241-MPAM-4 To: Fenghua Yu Cc: amitsinght@marvell.com, baisheng.gao@unisoc.com, baolin.wang@linux.alibaba.com, carl@os.amperecomputing.com, dave.martin@arm.com, david@kernel.org, dfustini@baylibre.com, gshan@redhat.com, james.morse@arm.com, jonathan.cameron@huawei.com, kobak@nvidia.com, lcherian@marvell.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, peternewman@google.com, punit.agrawal@oss.qualcomm.com, quic_jiles@quicinc.com, reinette.chatre@intel.com, rohit.mathew@arm.com, scott@os.amperecomputing.com, sdonthineni@nvidia.com, tan.shaopeng@fujitsu.com, xhao@linux.alibaba.com, catalin.marinas@arm.com, will@kernel.org, corbet@lwn.net, maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev References: <20260112165914.4086692-1-ben.horgan@arm.com> <20260112165914.4086692-46-ben.horgan@arm.com> <23f08379-301d-4ffc-bf6f-d6a7bb952724@nvidia.com> From: Ben Horgan Content-Language: en-US In-Reply-To: <23f08379-301d-4ffc-bf6f-d6a7bb952724@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Fenghua, On 1/15/26 23:20, Fenghua Yu wrote: > Hi, Shanker and Ben, > > On 1/12/26 08:59, Ben Horgan wrote: >> From: Shanker Donthineni >> >> In the T241 implementation of memory-bandwidth partitioning, in the >> absence >> of contention for bandwidth, the minimum bandwidth setting can affect the >> amount of achieved bandwidth. Specifically, the achieved bandwidth in the >> absence of contention can settle to any value between the values of >> MPAMCFG_MBW_MIN and MPAMCFG_MBW_MAX.  Also, if MPAMCFG_MBW_MIN is set >> zero (below 0.78125%), once a core enters a throttled state, it will >> never >> leave that state. >> >> The first issue is not a concern if the MPAM software allows to program >> MPAMCFG_MBW_MIN through the sysfs interface. This patch ensures program >> MBW_MIN=1 (0.78125%) whenever MPAMCFG_MBW_MIN=0 is programmed. > > When MBW_MIN=1, min mem bw can be very low when contention. This may > drop mem access performance. Is it possible to set MBW_MIN bigger so > that ensure the floor of mem access is high? Isn't that a policy decision rather than something we should be putting in a quirk framework? Thanks, Ben