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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 DB90EC49ED7 for ; Fri, 20 Sep 2019 10:45:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A720C2086A for ; Fri, 20 Sep 2019 10:45:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408680AbfITKpu (ORCPT ); Fri, 20 Sep 2019 06:45:50 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45084 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732138AbfITKpu (ORCPT ); Fri, 20 Sep 2019 06:45:50 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x8KAbPeV074196 for ; Fri, 20 Sep 2019 06:45:48 -0400 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0b-001b2d01.pphosted.com with ESMTP id 2v4t21701x-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 20 Sep 2019 06:45:48 -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) Fri, 20 Sep 2019 11:45:41 +0100 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x8KAje1A40108050 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 20 Sep 2019 10:45:40 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 630275204E; Fri, 20 Sep 2019 10:45:40 +0000 (GMT) Received: from localhost.localdomain (unknown [9.124.35.163]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id CAD065205A; Fri, 20 Sep 2019 10:45:37 +0000 (GMT) Subject: Re: Usecases for the per-task latency-nice attribute To: Qais Yousef Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Patrick Bellasi , subhra mazumdar , tim.c.chen@linux.intel.com, Valentin Schneider , mingo@redhat.com, morten.rasmussen@arm.com, dietmar.eggemann@arm.com, pjt@google.com, vincent.guittot@linaro.org, quentin.perret@arm.com, dhaval.giani@oracle.com, daniel.lezcano@linaro.org, tj@kernel.org, rafael.j.wysocki@intel.com References: <3e5c3f36-b806-5bcc-e666-14dc759a2d7b@linux.ibm.com> <20190919144259.vpuv7hvtqon4qgrv@e107158-lin.cambridge.arm.com> From: Parth Shah Date: Fri, 20 Sep 2019 16:15:37 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20190919144259.vpuv7hvtqon4qgrv@e107158-lin.cambridge.arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19092010-0012-0000-0000-0000034E7F76 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19092010-0013-0000-0000-00002189049F Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-09-20_03:,, 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=992 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1909200101 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/19/19 8:13 PM, Qais Yousef wrote: > On 09/18/19 18:11, Parth Shah wrote: >> Hello everyone, >> >> As per the discussion in LPC2019, new per-task property like latency-nice >> can be useful in certain scenarios. The scheduler can take proper decision >> by knowing latency requirement of a task from the end-user itself. >> >> There has already been an effort from Subhra for introducing Task >> latency-nice [1] values and have seen several possibilities where this type of >> interface can be used. >> >> From the best of my understanding of the discussion on the mail thread and >> in the LPC2019, it seems that there are two dilemmas; >> >> 1. Name: What should be the name for such attr for all the possible usecases? >> ============= >> Latency nice is the proposed name as of now where the lower value indicates >> that the task doesn't care much for the latency and we can spend some more >> time in the kernel to decide a better placement of a task (to save time, >> energy, etc.) >> But there seems to be a bit of confusion on whether we want biasing as well >> (latency-biased) or something similar, in which case "latency-nice" may >> confuse the end-user. >> >> 2. Value: What should be the range of possible values supported by this new >> attr? >> ============== >> The possible values of such task attribute still need community attention. >> Do we need a range of values or just binary/ternary values are sufficient? >> Also signed or unsigned and so the length of the variable (u64, s32, etc)? > > IMO the main question is who is the intended user of this new knob/API? > > If it's intended for system admins to optimize certain workloads on a system > then I like the latency-nice range. > > If we want to support application writers to define the latency requirements of > their tasks then I think latency-nice would be very confusing to use. > Especially when one has to consider they lack a pre-knowledge about the system > they will run on; and what else they are sharing the resources with. > Yes, valid point. But from my view, this will most certainly be for system admins who can optimize certain workloads from the systemd, tuned or similar OS daemons. >> >> >> >> This mail is to initiate the discussion regarding the possible usecases of >> such per task attribute and to come up with a specific name and value for >> the same. >> >> Hopefully, interested one should plot out their usecase for which this new >> attr can potentially help in solving or optimizing it. >> >> >> Well, to start with, here is my usecase. >> >> ------------------- >> **Usecases** >> ------------------- >> >> $> TurboSched >> ==================== >> TurboSched [2] tries to minimize the number of active cores in a socket by >> packing an un-important and low-utilization (named jitter) task on an >> already active core and thus refrains from waking up of a new core if >> possible. This requires tagging of tasks from the userspace hinting which >> tasks are un-important and thus waking-up a new core to minimize the >> latency is un-necessary for such tasks. >> As per the discussion on the posted RFC, it will be appropriate to use the >> task latency property where a task with the highest latency-nice value can >> be packed. >> But for this specific use-cases, having just a binary value to know which >> task is latency-sensitive and which not is sufficient enough, but having a >> range is also a good way to go where above some threshold the task can be >> packed. > > > $> EAS > ==================== > The new knob can help EAS path to switch to spreading behavior when > latency-nice is set instead of packing tasks on the most energy efficient CPU. > ie: pick the most energy efficient idle CPU. > +1 Thanks, Parth > -- > Qais Yousef >