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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 931A8C4321A for ; Fri, 28 Jun 2019 22:36:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4A96D208E3 for ; Fri, 28 Jun 2019 22:36:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="5VXljABH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727031AbfF1Wg1 (ORCPT ); Fri, 28 Jun 2019 18:36:27 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:37136 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726983AbfF1WgZ (ORCPT ); Fri, 28 Jun 2019 18:36:25 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x5SMYaNi081645; Fri, 28 Jun 2019 22:34:56 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=5BXhuEPFDddiNAekJ5I66ugIZ3EfVPNNcHP0UgKmH0Q=; b=5VXljABHIjidxf57ErkYPFevR2jYLr2wVGjAft6Mg6kxKJlEcuPUPxmVLLaSUNDB8snT MgP4XvSli4cRvyVCs9jRVuqvDJWTqFAo6g1+zej/pz18mozLa782ppJEPGz9G4y9AE6o rHS+NOIQYUgWWgwKGU1+MEt7B64GTiVOpP0Zpqks64FTacCvwIUrMrCkm/Wx4+VDWTct AcQ32t6H7CeIz5yGlhqDZceWBo1nWdkuPLRMaNKDx8BVQCYNRN3s6+JSUc8hYXz5YnwY F94fRkEapNe1cAdOrupa6iWPY8RcQmV7gkCp1rQeQ/JHauQv+ZSKg/slYWp+spezFIp1 Pg== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by userp2120.oracle.com with ESMTP id 2t9cyqyn13-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 28 Jun 2019 22:34:55 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x5SMXaR9104757; Fri, 28 Jun 2019 22:34:55 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3020.oracle.com with ESMTP id 2tat7e675n-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 28 Jun 2019 22:34:55 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x5SMYrei010475; Fri, 28 Jun 2019 22:34:54 GMT Received: from [10.132.91.175] (/10.132.91.175) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 28 Jun 2019 15:34:53 -0700 Subject: Re: [PATCH v3 5/7] sched: SIS_CORE to disable idle core search To: Parth Shah , linux-kernel@vger.kernel.org Cc: peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de, steven.sistare@oracle.com, dhaval.giani@oracle.com, daniel.lezcano@linaro.org, vincent.guittot@linaro.org, viresh.kumar@linaro.org, tim.c.chen@linux.intel.com, mgorman@techsingularity.net References: <20190627012919.4341-1-subhra.mazumdar@oracle.com> <20190627012919.4341-6-subhra.mazumdar@oracle.com> <0e0f3347-c262-2917-76d7-88dddf4e9122@linux.ibm.com> From: Subhra Mazumdar Message-ID: <59ab08d5-8b7c-00b9-230b-7c0b307a675f@oracle.com> Date: Fri, 28 Jun 2019 15:29:46 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <0e0f3347-c262-2917-76d7-88dddf4e9122@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9302 signatures=668688 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906280258 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9302 signatures=668688 X-Proofpoint-Spam-Details: rule=notspam policy=default 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-1906280259 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/28/19 12:01 PM, Parth Shah wrote: > > On 6/27/19 6:59 AM, subhra mazumdar wrote: >> Use SIS_CORE to disable idle core search. For some workloads >> select_idle_core becomes a scalability bottleneck, removing it improves >> throughput. Also there are workloads where disabling it can hurt latency, >> so need to have an option. >> >> Signed-off-by: subhra mazumdar >> --- >> kernel/sched/fair.c | 8 +++++--- >> 1 file changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index c1ca88e..6a74808 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6280,9 +6280,11 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) >> if (!sd) >> return target; >> >> - i = select_idle_core(p, sd, target); >> - if ((unsigned)i < nr_cpumask_bits) >> - return i; >> + if (sched_feat(SIS_CORE)) { >> + i = select_idle_core(p, sd, target); >> + if ((unsigned)i < nr_cpumask_bits) >> + return i; >> + } > This can have significant performance loss if disabled. The select_idle_core spreads > workloads quickly across the cores, hence disabling this leaves much of the work to > be offloaded to load balancer to move task across the cores. Latency sensitive > and long running multi-threaded workload should see the regression under this conditions. Yes in case of SPARC SMT8 I did notice that (see cover letter). That's why it is a feature that is ON by default, but can be turned OFF for specific workloads on x86 SMT2 that can benefit from it. > Also, systems like POWER9 has sd_llc as a pair of core only. So it > won't benefit from the limits and hence also hiding your code in select_idle_cpu > behind static keys will be much preferred. If it doesn't hurt then I don't see the point. Thanks, Subhra