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 A90D61459FD for ; Wed, 28 Aug 2024 09:00:19 +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=1724835624; cv=none; b=F35Mq5IjGzfeLb1zPCX/mAC9DRW9vb/oXa2M0Cl7edptssXBaF4BZLICEZNlWXnddnWba9+I7fLDCSLPSsSf8lLyaU7U4jd4U9dvWvrcDzbbk2634Crro2T8Wtk7GJymJ/IIDmzwtZhCfnQQ9Jc0/Y6CpJDmU7oCdci1cI5Nh6c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724835624; c=relaxed/simple; bh=SI3EKb/+2YCz9qQMJz1xHELer7He0gVsQNCnEVhOnDk=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=g6CUzWW81zY2knA1puRhpHepMW49laz6iw6rhyEf/zLo7jF9Tv9ttU1gyNKj4YLNGIfzhcESlGd+tVA9ocPYlx0JjeRhU61whh4J7tos1uzMmBhODMcpWM2oBYhvphiS08Cny+wPWRDn35PMOl4+bvvi+6rdSqCOrj/RYEpquyM= 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 [172.18.186.216]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4Wtyvw3YN2z6D9j0; Wed, 28 Aug 2024 16:57:00 +0800 (CST) Received: from lhrpeml500005.china.huawei.com (unknown [7.191.163.240]) by mail.maildlp.com (Postfix) with ESMTPS id DE8A1140447; Wed, 28 Aug 2024 17:00:16 +0800 (CST) Received: from localhost (10.203.177.66) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.39; Wed, 28 Aug 2024 10:00:16 +0100 Date: Wed, 28 Aug 2024 10:00:15 +0100 From: Jonathan Cameron To: Dave Jiang CC: , , , , , Subject: Re: [PATCH v7 3/3] cxl: Add documentation to explain the shared link bandwidth calculation Message-ID: <20240828100015.000010a0@Huawei.com> In-Reply-To: <3c325ad2-e483-417a-a952-1357df3382c4@intel.com> References: <20240710222716.797267-1-dave.jiang@intel.com> <20240710222716.797267-4-dave.jiang@intel.com> <20240827170640.000007ab@Huawei.com> <3c325ad2-e483-417a-a952-1357df3382c4@intel.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-cxl@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: lhrpeml500005.china.huawei.com (7.191.163.240) To lhrpeml500005.china.huawei.com (7.191.163.240) On Tue, 27 Aug 2024 15:38:27 -0700 Dave Jiang wrote: > On 8/27/24 9:06 AM, Jonathan Cameron wrote: > > On Wed, 10 Jul 2024 15:24:02 -0700 > > Dave Jiang wrote: > > > >> Create a kernel documentation to describe how the CXL shared upstream > >> link bandwidth is calculated. > >> > >> Suggested-by: Dan Williams > >> Signed-off-by: Dave Jiang > > Oops. Missed this previously. A few minor things inline. > > > > J > >> --- > >> .../driver-api/cxl/access-coordinates.rst | 90 +++++++++++++++++++ > >> Documentation/driver-api/cxl/index.rst | 1 + > >> MAINTAINERS | 1 + > >> 3 files changed, 92 insertions(+) > >> create mode 100644 Documentation/driver-api/cxl/access-coordinates.rst > >> > >> diff --git a/Documentation/driver-api/cxl/access-coordinates.rst b/Documentation/driver-api/cxl/access-coordinates.rst > >> new file mode 100644 > >> index 000000000000..973e63872f06 > >> --- /dev/null > >> +++ b/Documentation/driver-api/cxl/access-coordinates.rst > >> @@ -0,0 +1,90 @@ > >> +.. SPDX-License-Identifier: GPL-2.0 > >> +.. include:: > >> + > >> +================================== > >> +CXL Access Coordinates Computation > >> +================================== > >> + > >> +Shared Upstream Link Calculation > >> +================================ > >> +For certain CXL region construction with endpoints behind CXL switches (SW) or > >> +Root Ports (RP), there is the possibility of the total bandwdith for all > > spell check. bandwidth > >> +the endpoints behind a switch being more than the switch upstream link. > > > > Could also be the Generic Port bit of the topology. Mind you I'm still failing > > to come up with text for the qemu GP Documentation that the reviewers can follow > > so maybe that's just too hard to describe here. Could use weasel words. > > > > "A similar situation can occur within the host, upstream of the root ports." > > > > > >> +The CXL driver performs an additional pass after all the targets have > >> +arrived for a region in order to recalculate the bandwidths with possible > >> +upstream link being a limiting factor in mind. > >> + > >> +The algorithm assumes the configuration is a symmetric topology as that > >> +maximizes performance. When asymmetric topology is detected, the calculation > >> +is aborted when such topology is detected. An asymmetric topology is detected > > > > is detected is duplicated. > > I don't follow here. > >+ When asymmetric topology is detected, the calculation ^^^^^^^^^^^ >+is aborted when such topology is detected. ^^^^^^^^^^^^ Delete the second one. > > > >> +during topology walk where the number of RPs detected as a grandparent is not > >> +equal to the number of devices iterated in the same iteration loop. > > > > Maybe make the point that asymmetric in terms of only properties of devices > > is not detected. It just uses the first one I think? > > I also don't follow here. > > I also wonder if I should use "unbalanced" topology rather than "unsymmetric"? Difference between detecting a topology with different number of links and one where say one type 3 device in an interleave set has lower bandwidth in it's CDAT. IIRC this does the first, but not the second. > > DJ