From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f198.google.com (mail-pg1-f198.google.com [209.85.215.198]) by kanga.kvack.org (Postfix) with ESMTP id 1F4996B42E2 for ; Mon, 26 Nov 2018 12:20:07 -0500 (EST) Received: by mail-pg1-f198.google.com with SMTP id l131so8216604pga.2 for ; Mon, 26 Nov 2018 09:20:07 -0800 (PST) Received: from mga02.intel.com (mga02.intel.com. [134.134.136.20]) by mx.google.com with ESMTPS id a28si902880pgl.530.2018.11.26.09.20.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Nov 2018 09:20:05 -0800 (PST) Subject: Re: [PATCH 0/7] ACPI HMAT memory sysfs representation References: <20181114224902.12082-1-keith.busch@intel.com> <1ed406b2-b85f-8e02-1df0-7c39aa21eca9@arm.com> <4ea6e80f-80ba-6992-8aa0-5c2d88996af7@intel.com> <9015e51a-3584-7bb2-cc5e-25b0ec8e5494@intel.com> <1a9e887b-8087-e897-6195-e8df325bd458@arm.com> From: Dave Hansen Message-ID: <3b86c5c5-53f2-29bf-48e7-5749c7287dca@intel.com> Date: Mon, 26 Nov 2018 09:20:04 -0800 MIME-Version: 1.0 In-Reply-To: <1a9e887b-8087-e897-6195-e8df325bd458@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Anshuman Khandual , Keith Busch , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-mm@kvack.org Cc: Greg Kroah-Hartman , Rafael Wysocki , Dan Williams On 11/26/18 7:38 AM, Anshuman Khandual wrote: > On 11/24/2018 12:51 AM, Dave Hansen wrote: >> On 11/22/18 10:42 PM, Anshuman Khandual wrote: >>> Are we willing to go in the direction for inclusion of a new system >>> call, subset of it appears on sysfs etc ? My primary concern is not >>> how the attribute information appears on the sysfs but lack of it's >>> completeness. >> >> A new system call makes total sense to me. I have the same concern >> about the completeness of what's exposed in sysfs, I just don't see a >> _route_ to completeness with sysfs itself. Thus, the minimalist >> approach as a first step. > > Okay if we agree on the need for a new specific system call extracting > the superset attribute information MAX_NUMNODES * MAX_NUMNODES * U64 > (u64 packs 8 bit values for 8 attributes or something like that) as we > had discussed before, it makes sense to export a subset of it which can > be faster but useful for the user space without going through a system > call. The information that needs to be exported is a bit more than that. It's not just a binary attribute. The information we have from the new ACPI table, for instance, is the read and write bandwidth and latency between two nodes. They are, IIRC, two-byte values in the ACPI table[1], each. That's 8 bytes worth of data right there, which wouldn't fit *anything* else. The list of things we want to export will certainly grow. That means we need a syscall something like this: int get_mem_attribute(unsigned long attribute_nr, unsigned long __user * initiator_nmask, unsigned long __user * target_nmask, unsigned long maxnode, unsigned long *attributes_out); #define MEM_ATTR_READ_BANDWIDTH 1 #define MEM_ATTR_WRITE_BANDWIDTH 2 #define MEM_ATTR_READ_LATENCY 3 #define MEM_ATTR_WRITE_LATENCTY 4 #define MEM_ATTR_ENCRYPTION 5 If you want to know the read latency between nodes 4 and 8, you do: ret = get_mem_attr(MEM_ATTR_READ_LATENCY, (1<<4), (1<<8), max, &array); And the answer shows up at array[0] in this example. If you had more than one bit set in the two nmasks, you would have a longer array. The length of the array is the number of bits set in initiator_nmask * the number of bits set in target_nmask * sizeof(ulong). This has the advantage of supporting ULONG_MAX attributes, and scales from asking for one attribute at a time all the way up to dumping the entire system worth of data for a single attribute. The only downside is that it's one syscall per attribute instead of packing them all together. But, if we have a small enough number to pack them in one ulong, then I think we can make 64 syscalls without too much trouble. > Do you agree on a (system call + sysfs) approach in principle ? > Also sysfs exported information has to be derived from whats available > through the system call not the other way round. Hence the starting > point has to be the system call definition. Both the sysfs information *and* what will be exported in any future interfaces are derived from platform-specific information. They are not derived from one _interface_ or the other. They obviously need to be consistent, though. 1. See "Table 5-142 System Locality Latency and Bandwidth Information Structure" here: http://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdf