From nobody Sat Feb 7 16:06:27 2026 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.13]) (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 22D3D634FD; Fri, 22 Mar 2024 18:20:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.13 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711131624; cv=none; b=R+z8hzBhrKCaed7LyHuzgyjmQ9F0mcfcho0EkIEhevjkqDDVrh0z3sycc/QTso5ed5udQEItIRp8SADKX+LHWuTx684iCvgjhJqWXPg3mYich3yODVVJLAxBPtqLbwI9YM6BbjdPzJ2giE4mk3D4xTD6jvOhTIDQyGnZHR+1OBs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711131624; c=relaxed/simple; bh=zaoJUGsUnomu4sLnNHkQa13VzSoMT7EmbpbB5GpjhMQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=VOE3e4rDGUKagyq4xKfL2B59Tkalj94QLn7lRRM7M/6/+onPyxCGPorVRxGAUJN6rccREXil12VVFdX1s0XsC2bkqjdk2SuLj1rnnPRe3vtg8JuT60q0kz/mmc7cxMjrZanrKZQQzQZyiXzdi04DK8D7fNVTXEMeIG704Zq2j2k= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=Stp1eWWK; arc=none smtp.client-ip=198.175.65.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Stp1eWWK" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1711131624; x=1742667624; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=zaoJUGsUnomu4sLnNHkQa13VzSoMT7EmbpbB5GpjhMQ=; b=Stp1eWWKfOt1xwGEOFO2ueATFQgh7J6mBLdnODxxlRKpdiQVZ9+isOkQ +7RlBn7Mb0+wZAvfYniuTVIHfgXxXwL0mR0nKBThzwPpnEeMGli8ykN7a cWm1AJCZdsutHXziiVQHi2LSWYeJBINXJv+lpxMe+ai5pa02UVLC5VMPj 8jfNRl53GBrPcEYCsN1dmsUye8nd4XJ53RW2jD6H1LlTkSXg0+1mZQk70 V5MjzJENloN9veDnxkMV3PWLSf3W5FMKnnV+Xmx8O/utNoz9VhVUL7TwC oNmTKwQskzBcN6tOaGN5unXKuK/OWb3exXKT8ZNwGY1AQeOy99QsHHT9h g==; X-IronPort-AV: E=McAfee;i="6600,9927,11020"; a="17339800" X-IronPort-AV: E=Sophos;i="6.07,146,1708416000"; d="scan'208";a="17339800" Received: from orviesa009.jf.intel.com ([10.64.159.149]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Mar 2024 11:20:23 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,146,1708416000"; d="scan'208";a="15000969" Received: from agluck-desk3.sc.intel.com ([172.25.222.105]) by orviesa009-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Mar 2024 11:20:22 -0700 From: Tony Luck To: linux-doc@vger.kernel.org Cc: Fenghua Yu , Reinette Chatre , Peter Newman , James Morse , Babu Moger , Drew Fustini , x86@kernel.org, linux-kernel@vger.kernel.org, patches@lists.linux.dev, Tony Luck Subject: [PATCH] Documentation/x86: Document resctrl bandwidth control units are MiB Date: Fri, 22 Mar 2024 11:20:15 -0700 Message-ID: <20240322182016.196544-1-tony.luck@intel.com> X-Mailer: git-send-email 2.44.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The memory bandwidth software controller uses 2^20 units rather than 10^6. See mbm_bw_count() which computes bandwidth using the "SZ_1M" Linux define for 0x00100000. Update the documentation to use MiB when describing this feature. It's too late to fix the mount option "mba_MBps" as that is now an established user interface. Signed-off-by: Tony Luck --- Documentation/arch/x86/resctrl.rst | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/re= sctrl.rst index a6279df64a9d..3712d81cb50c 100644 --- a/Documentation/arch/x86/resctrl.rst +++ b/Documentation/arch/x86/resctrl.rst @@ -45,7 +45,7 @@ mount options are: Enable code/data prioritization in L2 cache allocations. "mba_MBps": Enable the MBA Software Controller(mba_sc) to specify MBA - bandwidth in MBps + bandwidth in MiBps "debug": Make debug files accessible. Available debug files are annotated with "Available only with debug option". @@ -526,7 +526,7 @@ threads start using more cores in an rdtgroup, the actu= al bandwidth may increase or vary although user specified bandwidth percentage is same. =20 In order to mitigate this and make the interface more user friendly, -resctrl added support for specifying the bandwidth in MBps as well. The +resctrl added support for specifying the bandwidth in MiBps as well. The kernel underneath would use a software feedback mechanism or a "Software Controller(mba_sc)" which reads the actual bandwidth using MBM counters and adjust the memory bandwidth percentages to ensure:: @@ -573,13 +573,13 @@ Memory b/w domain is L3 cache. =20 MB:=3Dbandwidth0;=3Dbandwidth1;... =20 -Memory bandwidth Allocation specified in MBps +Memory bandwidth Allocation specified in MiBps --------------------------------------------- =20 Memory bandwidth domain is L3 cache. :: =20 - MB:=3Dbw_MBps0;=3Dbw_MBps1;... + MB:=3Dbw_MiBps0;=3Dbw_MiBps1;... =20 Slow Memory Bandwidth Allocation (SMBA) --------------------------------------- --=20 2.44.0