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 2D842C5516D for ; Fri, 31 Jul 2026 17:54:13 +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=GU+tsc+RzMuyFa7007MrWHfZ9LjITE8iUwHkl/UCfAM=; b=smmNlMnffAJm5s+xTxEt/D+clI HoVVRxOjRjzisX41DIwSsVaJZ09Oh67q89XlhWdSnAgBg/ZnG7JxrbIU0jbFVp6PYf43M7CHKuctL D1iN4rv9TEvH3GMQXs3HqFlpRPHcMbXQa+ihq9xMooF7EV0eCPXe6koskMnwmXI6iDDJ79O3DM9lU 9tozbdZnd5/WBclgEfPIlmXJzMlWh7EMLB5AKna3ODO+ZX8QuTP7cdjuPJeW3cHD8UEl17Oa+IXfq wSYxteBx04N3Ts01U9dU0ahL7lx80rpT6r0lfPdwGxtNyiWX+uGiy57Vc87KHbG/B5ACS9VBNw/wp AiFxwJig==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wprQQ-0000000DIr6-3jjT; Fri, 31 Jul 2026 17:53:38 +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 1wprPw-0000000DIaZ-3Bjb for linux-arm-kernel@lists.infradead.org; Fri, 31 Jul 2026 17:53:10 +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 A4A031595; Fri, 31 Jul 2026 10:53:03 -0700 (PDT) Received: from e134344.cambridge.arm.com (e134344.arm.com [10.2.212.8]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 020CE3F66F; Fri, 31 Jul 2026 10:53:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785520387; bh=6EfGYUXnKKBHHuYowjEcCKBALcv0osir6Ea6z6Kf8rE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pTLCEDE1Ps8dQVe4Hox+3nPTmum8Kyyex0QDAF+Bip2eNzX4XM1J/FeR34SJzI+SF 9snuoxNt7sNekDBi3bK8h+gPFygWO+RnGWm5FylJoKgj/fkIrjHy2XEHPMJawZheV5 WxomhmEYFyWUoDcOovpb4H1ZxgjaWR/RR1jELB1A= From: Ben Horgan To: ben.horgan@arm.com, will@kernel.org Cc: james.morse@arm.com, fenghuay@nvidia.com, linux-arm-kernel@lists.infradead.org, andre.przywara@arm.com, gshan@redhat.com, tan.shaopeng@jp.fujitsu.com, sdonthineni@nvidia.com, jonathan.cameron@oss.qualcomm.com Subject: [PATCH 5/6] arm64: mpam: Add memory bandwidth usage (MBWU) documentation Date: Fri, 31 Jul 2026 18:52:42 +0100 Message-ID: <20260731175243.904730-6-ben.horgan@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260731175243.904730-1-ben.horgan@arm.com> References: <20260731175243.904730-1-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-20260731_105309_245180_96FAEEAF X-CRM114-Status: GOOD ( 14.01 ) 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 Reviewed-by: Shaopeng Tan Reviewed-by: Fenghua Yu Reviewed-by: Gavin Shan --- Changes since v4: Add paragraph about the future. Changes since v5: Add R-b's from Fenghua and Gavin --- Documentation/arch/arm64/mpam.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/Documentation/arch/arm64/mpam.rst b/Documentation/arch/arm64/mpam.rst index 570f51a8d4eb..67fe515ed501 100644 --- a/Documentation/arch/arm64/mpam.rst +++ b/Documentation/arch/arm64/mpam.rst @@ -65,6 +65,28 @@ 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. (The platform 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. + + All these restrictions based on L3 cache are due to resctrl, currently, only + supporting monitoring at the L3 scope. It is expected that going forward more + MBWU monitors can be exposed to the user after support for more monitoring + scopes is added to resctrl. + Reporting Bugs ============== If you are not seeing the counters or controls you expect please share the -- 2.43.0