From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D2DAF33EAEB for ; Tue, 6 Jan 2026 15:20:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.176.79.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767712822; cv=none; b=WQjsjKpybhdeaSAyEhRxw5hTmf/bQxWbjAFsz3ohJ3gTXQRI0V+BWIvH6v2SNuxM0sImP5SM41LDTjX3FZcsmauDwr3EPx8kvjqnBy6PowGROcKlGwH1VIX77AxdKts3L42PgfxlbiI/6lMQZFSgiyzZDieRim5VBNbJZVwp1U0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767712822; c=relaxed/simple; bh=aI9uvvTfImakEhrHj5ybUw75fkaNSglPQJnN8REAxOM=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ia5uZbS9viR4bFktJYoKuIzUSOz4HjwjIoVfc5AobQ9f0sUpY227FLC7RicI6HvHL6sGKMCAjjjcrz+pYMSyfkgMQerRYQ30bpEnEAGV/zYzvTVrdfMy2nflGNyoNtjVGxrJGewi8miXRhFLJzfe2+xJ/7fBcxOUuEyebXfhYPA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=185.176.79.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.18.224.83]) by frasgout.his.huawei.com (SkyGuard) with ESMTPS id 4dlvxB4gfBzJ469c; Tue, 6 Jan 2026 23:20:14 +0800 (CST) Received: from dubpeml100005.china.huawei.com (unknown [7.214.146.113]) by mail.maildlp.com (Postfix) with ESMTPS id 636E640086; Tue, 6 Jan 2026 23:20:16 +0800 (CST) Received: from localhost (10.195.245.156) by dubpeml100005.china.huawei.com (7.214.146.113) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.36; Tue, 6 Jan 2026 15:20:14 +0000 Date: Tue, 6 Jan 2026 15:20:11 +0000 From: Jonathan Cameron To: Ben Horgan CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 43/45] arm_mpam: Add workaround for T241-MPAM-4 Message-ID: <20260106152011.000047ba@huawei.com> In-Reply-To: <20251219181147.3404071-44-ben.horgan@arm.com> References: <20251219181147.3404071-1-ben.horgan@arm.com> <20251219181147.3404071-44-ben.horgan@arm.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: lhrpeml500010.china.huawei.com (7.191.174.240) To dubpeml100005.china.huawei.com (7.214.146.113) On Fri, 19 Dec 2025 18:11:45 +0000 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 cocern if the MPAM software allows to program concern > MPAMCFG_MBW_MIN through the sysfs interface. This patch ensures program > MBW_MIN=1 (0.78125%) whenever MPAMCFG_MBW_MIN=0 is programmed. > > In the scenario where the resctrl doesn't support the MBW_MIN interface via > sysfs, to achieve bandwidth closer to MW_MAX in the absence of contention, MBW_MAX > software should configure a relatively narrow gap between MBW_MIN and > MBW_MAX. The recommendation is to use a 5% gap to mitigate the problem. > > [ morse: Added as second quirk, adapted to use the new intermediate values > in mpam_extend_config() ] > > Signed-off-by: Shanker Donthineni > Signed-off-by: James Morse > Signed-off-by: Ben Horgan > --- > Changes since rfc: > MPAM_IIDR_NVIDIA_T421 -> MPAM_IIDR_NVIDIA_T241 > Handling when reset_mbw_min is set > --- > Documentation/arch/arm64/silicon-errata.rst | 2 + > drivers/resctrl/mpam_devices.c | 59 +++++++++++++++------ > drivers/resctrl/mpam_internal.h | 1 + > 3 files changed, 46 insertions(+), 16 deletions(-) > > diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst > index 4e86b85fe3d6..b18bc704d4a1 100644 > --- a/Documentation/arch/arm64/silicon-errata.rst > +++ b/Documentation/arch/arm64/silicon-errata.rst > @@ -248,6 +248,8 @@ stable kernels. > +----------------+-----------------+-----------------+-----------------------------+ > | NVIDIA | T241 MPAM | T241-MPAM-1 | N/A | > +----------------+-----------------+-----------------+-----------------------------+ > +| NVIDIA | T241 MPAM | T241-MPAM-4 | N/A | > ++----------------+-----------------+-----------------+-----------------------------+ > +----------------+-----------------+-----------------+-----------------------------+ > | Freescale/NXP | LS2080A/LS1043A | A-008585 | FSL_ERRATUM_A008585 | > +----------------+-----------------+-----------------+-----------------------------+