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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AC827C43387 for ; Thu, 10 Jan 2019 12:37:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88833214DA for ; Thu, 10 Jan 2019 12:37:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728459AbfAJMhP (ORCPT ); Thu, 10 Jan 2019 07:37:15 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57280 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727944AbfAJMhO (ORCPT ); Thu, 10 Jan 2019 07:37:14 -0500 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id x0ACa0k9036627 for ; Thu, 10 Jan 2019 07:37:13 -0500 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 2px4835m64-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 10 Jan 2019 07:37:12 -0500 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 10 Jan 2019 12:37:10 -0000 Received: from b06cxnps4075.portsmouth.uk.ibm.com (9.149.109.197) by e06smtp05.uk.ibm.com (192.168.101.135) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 10 Jan 2019 12:37:07 -0000 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x0ACb6Wo65536032 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 10 Jan 2019 12:37:06 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 50927A405F; Thu, 10 Jan 2019 12:37:06 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4ABB0A405B; Thu, 10 Jan 2019 12:37:04 +0000 (GMT) Received: from skywalker.linux.ibm.com (unknown [9.199.54.61]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 10 Jan 2019 12:37:04 +0000 (GMT) X-Mailer: emacs 26.1 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: Keith Busch , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-mm@kvack.org Cc: Greg Kroah-Hartman , Rafael Wysocki , Dave Hansen , Dan Williams , Keith Busch Subject: Re: [PATCHv3 07/13] node: Add heterogenous memory access attributes In-Reply-To: <20190109174341.19818-8-keith.busch@intel.com> References: <20190109174341.19818-1-keith.busch@intel.com> <20190109174341.19818-8-keith.busch@intel.com> Date: Thu, 10 Jan 2019 18:07:02 +0530 MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 x-cbid: 19011012-0020-0000-0000-000003045E6F X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19011012-0021-0000-0000-0000215561FA Message-Id: <87y37sit8x.fsf@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-10_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901100103 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Keith Busch writes: > Heterogeneous memory systems provide memory nodes with different latency > and bandwidth performance attributes. Provide a new kernel interface for > subsystems to register the attributes under the memory target node's > initiator access class. If the system provides this information, applications > may query these attributes when deciding which node to request memory. > > The following example shows the new sysfs hierarchy for a node exporting > performance attributes: > > # tree -P "read*|write*" /sys/devices/system/node/nodeY/classZ/ > /sys/devices/system/node/nodeY/classZ/ > |-- read_bandwidth > |-- read_latency > |-- write_bandwidth > `-- write_latency > > The bandwidth is exported as MB/s and latency is reported in nanoseconds. > Memory accesses from an initiator node that is not one of the memory's > class "Z" initiator nodes may encounter different performance than > reported here. When a subsystem makes use of this interface, initiators > of a lower class number, "Z", have better performance relative to higher > class numbers. When provided, class 0 is the highest performing access > class. How does the definition of performance relate to bandwidth and latency here?. The initiator in this class has the least latency and high bandwidth? Can there be a scenario where both are not best for the same node? ie, for a target Node Y, initiator Node A gives the highest bandwidth but initiator Node B gets the least latency. How such a config can be represented? Or is that not possible? -aneesh