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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 95F61C43334 for ; Wed, 5 Sep 2018 11:14:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4B8C920861 for ; Wed, 5 Sep 2018 11:14:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4B8C920861 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.vnet.ibm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727592AbeIEPoa (ORCPT ); Wed, 5 Sep 2018 11:44:30 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:35780 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725868AbeIEPoa (ORCPT ); Wed, 5 Sep 2018 11:44:30 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w85BEVcd009442 for ; Wed, 5 Sep 2018 07:14:43 -0400 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0b-001b2d01.pphosted.com with ESMTP id 2macndvky5-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 05 Sep 2018 07:14:43 -0400 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 5 Sep 2018 12:14:38 +0100 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w85BEblK43909220 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 5 Sep 2018 11:14:37 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A75F84C04E; Wed, 5 Sep 2018 14:14:32 +0100 (BST) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C12824C040; Wed, 5 Sep 2018 14:14:31 +0100 (BST) Received: from linux.vnet.ibm.com (unknown [9.40.192.68]) by d06av22.portsmouth.uk.ibm.com (Postfix) with SMTP; Wed, 5 Sep 2018 14:14:31 +0100 (BST) Date: Wed, 5 Sep 2018 04:14:36 -0700 From: Srikar Dronamraju To: Vincent Guittot Cc: Peter Zijlstra , Ingo Molnar , linux-kernel Subject: Re: [RFC PATCH 3/4] sched/topology: remove smt_gain Reply-To: Srikar Dronamraju References: <1535548752-4434-1-git-send-email-vincent.guittot@linaro.org> <1535548752-4434-4-git-send-email-vincent.guittot@linaro.org> <20180904082424.GA2090@linux.vnet.ibm.com> <20180904093626.GA23936@linaro.org> <20180904103742.GC61288@linux.vnet.ibm.com> <20180905085029.GA57420@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 18090511-0012-0000-0000-000002A4184D X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18090511-0013-0000-0000-000020D839B0 Message-Id: <20180905111436.GB57420@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-09-05_06:,, 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=789 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1809050120 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Vincent Guittot [2018-09-05 11:11:35]: > On Wed, 5 Sep 2018 at 10:50, Srikar Dronamraju > wrote: > > > > * Vincent Guittot [2018-09-05 09:36:42]: > > > > > > > > > > I dont know of any systems that have come with single threaded and > > > > multithreaded. However some user can still offline few threads in a core > > > > while leaving other cores untouched. I dont really know why somebody > > > > would want to do it. For example, some customer was toying with SMT 3 > > > > mode in a SMT 8 power8 box. > > > > > > In this case, it means that we have the same core capacity whatever > > > the number of CPUs > > > and a core with SMT 3 will be set with the same compute capacity as > > > the core with SMT 8. > > > Does it still make sense ? > > > > > > > To me it make sense atleast from a power 8 perspective, because SMT 1 > > > SMT 2 > SMT 4 > SMT8. So if one core is configured for SMT 2 and other > > core is configured for SMT4; all threads being busy, the individual > > threads running on SMT2 core will complete more work than SMT 4 core > > threads. > > I agree for individual thread capacity but at core group level, the > core SMT 1 will have the same capacity as core group SMT 8 so load > balance will try to balance evenly the tasks between the 2 cores > whereas core SMT 8 > core SMT1 , isn't it ? > I believe that Core capacity irrespective of the number of threads should be similar. We wanted to give a small benefit if the core has multiple threads and that was smt_gain. Lets say we have 8 equal sw threads running on 2 cores; one being SMT 2 and other being SMT4. then 4 threads should be spread to each core. So that we would be fair to each of the 8 SW threads. -- Thanks and Regards Srikar Dronamraju