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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E434FCD5BAB for ; Wed, 20 May 2026 21:25:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9XTWxwwyFRV0edc/CsRaOQfQYJO3vq7buLBrqA+5Rcc=; b=iGiCq8e3WsB+7CSSGcHiUUfq3f wTtGMLncAFcl5VdNsPMdrMWf3FmZ6uh6VT2QSWMkXxE/8oINo+NBIC6B1pGeMu2wTxTzXalUCLuq+ rQ8zncMdV0eOIw/MicNLoIL0g7Sc1HLaDpgj78gnGZdreal/fR55iGoOzq7NZZNXzjfPvyhz4I8Sw m7mpP3bXqDjjd3sXll1MVXZMaKAwX6Q5CPqMPHvB9ZW9VG1SOoLPZvLZgEQiF2bU2AedAvPsTo71O hpybBLsFPeBwgOIfAbKkWDy7J4yBmyFrf4Ul0i3NvjmoQEt59o8D51pOWP6y9WTJLrmLx62gisilN 6kX8sjBg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPoQF-00000005pwX-3Pi5; Wed, 20 May 2026 21:25:47 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPoQC-00000005ptM-0VI1 for linux-arm-kernel@lists.infradead.org; Wed, 20 May 2026 21:25:45 +0000 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 D9E964923; Wed, 20 May 2026 14:25:37 -0700 (PDT) Received: from e134344.cambridge.arm.com (e134344.arm.com [10.1.196.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id B294C3F632; Wed, 20 May 2026 14:25:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779312343; bh=wIKzf5ul/e8eANNandonrCHt67Qv+ziekknEc/tHdes=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bqBW2ZxuSoMTm02aZ9wHS6bdFRPTNmNOahYi2pDBykKswCPmhIM7GOJbjpQ4Sr4/k pAocUen0g9FFhjKaZMpY8cB2UTsYg8Ky5Nr8vQDcbxQ22K5Q3ev0+yF3I2+Nh0cER/ 74WMZgz1l/IchZcXy2P3SoDq2Ji1bnraVDmba7Uo= From: Ben Horgan To: ben.horgan@arm.com 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, fenghuay@nvidia.com, gshan@redhat.com, james.morse@arm.com, jic23@kernel.org, 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, zengheng4@huawei.com, x86@kernel.org Subject: [PATCH v4 5/5] arm64: mpam: Add memory bandwidth usage (MBWU) documentation Date: Wed, 20 May 2026 22:24:58 +0100 Message-ID: <20260520212458.1797221-6-ben.horgan@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260520212458.1797221-1-ben.horgan@arm.com> References: <20260520212458.1797221-1-ben.horgan@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260520_142544_201289_2AEACA6B X-CRM114-Status: GOOD ( 12.83 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Memory bandwidth monitoring make uses of MBWU monitors and is now exposed to the user via resctrl. Add some documentation so the user knows what to expect. Co-developed-by: James Morse Signed-off-by: James Morse Signed-off-by: Ben Horgan --- Documentation/arch/arm64/mpam.rst | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/Documentation/arch/arm64/mpam.rst b/Documentation/arch/arm64/mpam.rst index 570f51a8d4eb..208ff17068c4 100644 --- a/Documentation/arch/arm64/mpam.rst +++ b/Documentation/arch/arm64/mpam.rst @@ -65,6 +65,23 @@ The supported features are: there is at least one CSU monitor on each MSC that makes up the L3 group. Exposing CSU counters from other caches or devices is not supported. +* Memory Bandwidth Usage (MBWU) on or after the L3 cache. resctrl uses the + L3 cache-id to identify where the memory bandwidth is measured. For this + reason the platform must have an L3 cache with cache-id's supplied by + firmware. (It doesn't need to support MPAM.) + + Memory bandwidth monitoring makes use of MBWU monitors in each MSC that + makes up the L3 group. If the memory bandwidth monitoring is on the memory + rather than the L3 then there must be a single global L3 as otherwise it + is unknown which L3 the traffic came from. + + To expose 'mbm_total_bytes', the topology of the group of MSC chosen must + match the topology of the L3 cache so that the cache-id's can be + repainted. For example: Platforms with Memory bandwidth monitors on + CPU-less NUMA nodes cannot expose 'mbm_total_bytes' as these nodes do not + have a corresponding L3 cache. 'mbm_local_bytes' is not exposed as MPAM + cannot distinguish local traffic from global traffic. + Reporting Bugs ============== If you are not seeing the counters or controls you expect please share the -- 2.43.0