From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by kanga.kvack.org (Postfix) with ESMTP id A35106B076F for ; Fri, 9 Nov 2018 22:48:22 -0500 (EST) Received: by mail-wr1-f72.google.com with SMTP id j6-v6so3414232wre.1 for ; Fri, 09 Nov 2018 19:48:22 -0800 (PST) Received: from g2t2352.austin.hpe.com (g2t2352.austin.hpe.com. [15.233.44.25]) by mx.google.com with ESMTPS id z2-v6si7670725wrv.437.2018.11.09.19.48.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Nov 2018 19:48:21 -0800 (PST) From: "Elliott, Robert (Persistent Memory)" Subject: RE: [RFC PATCH v4 11/13] mm: parallelize deferred struct page initialization within each node Date: Sat, 10 Nov 2018 03:48:14 +0000 Message-ID: References: <20181105165558.11698-1-daniel.m.jordan@oracle.com> <20181105165558.11698-12-daniel.m.jordan@oracle.com> In-Reply-To: <20181105165558.11698-12-daniel.m.jordan@oracle.com> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Daniel Jordan , "linux-mm@kvack.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Cc: "aarcange@redhat.com" , "aaron.lu@intel.com" , "akpm@linux-foundation.org" , "alex.williamson@redhat.com" , "bsd@redhat.com" , "darrick.wong@oracle.com" , "dave.hansen@linux.intel.com" , "jgg@mellanox.com" , "jwadams@google.com" , "jiangshanlai@gmail.com" , "mhocko@kernel.org" , "mike.kravetz@oracle.com" , "Pavel.Tatashin@microsoft.com" , "prasad.singamsetty@oracle.com" , "rdunlap@infradead.org" , "steven.sistare@oracle.com" , "tim.c.chen@intel.com" , "tj@kernel.org" , "vbabka@suse.cz" > -----Original Message----- > From: linux-kernel-owner@vger.kernel.org owner@vger.kernel.org> On Behalf Of Daniel Jordan > Sent: Monday, November 05, 2018 10:56 AM > Subject: [RFC PATCH v4 11/13] mm: parallelize deferred struct page > initialization within each node >=20 > ... The kernel doesn't > know the memory bandwidth of a given system to get the most efficient > number of threads, so there's some guesswork involved. =20 The ACPI HMAT (Heterogeneous Memory Attribute Table) is designed to report that kind of information, and could facilitate automatic tuning. There was discussion last year about kernel support for it: https://lore.kernel.org/lkml/20171214021019.13579-1-ross.zwisler@linux.inte= l.com/ > In testing, a reasonable value turned out to be about a quarter of the > CPUs on the node. ... > + /* > + * We'd like to know the memory bandwidth of the chip to > calculate the > + * most efficient number of threads to start, but we can't. > + * In testing, a good value for a variety of systems was a > quarter of the CPUs on the node. > + */ > + nr_node_cpus =3D DIV_ROUND_UP(cpumask_weight(cpumask), 4); You might want to base that calculation on and limit the threads to physical cores, not hyperthreaded cores. --- Robert Elliott, HPE Persistent Memory