From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755890AbcETNE2 (ORCPT ); Fri, 20 May 2016 09:04:28 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:56072 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752668AbcETNE0 (ORCPT ); Fri, 20 May 2016 09:04:26 -0400 X-Greylist: delayed 2423 seconds by postgrey-1.27 at vger.kernel.org; Fri, 20 May 2016 09:04:26 EDT Message-Id: <201605201223.u4KCNaTI025072@mx0a-001b2d01.pphosted.com> X-IBM-Helo: d28dlp03.in.ibm.com X-IBM-MailFrom: shilpa.bhat@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org;linux-pm@vger.kernel.org Date: Fri, 20 May 2016 17:53:41 +0530 From: Shilpasri G Bhat User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Peter Zijlstra CC: "Rafael J. Wysocki" , Viresh Kumar , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List , "Gautham R. Shenoy" , shreyas@linux.vnet.ibm.com, akshay.adiga@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org, Steve Muckle Subject: Re: [RFC PATCH] Increase in idle power with schedutil References: <1463576020-18597-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com> <20160519114029.GW3193@twins.programming.kicks-ass.net> In-Reply-To: <20160519114029.GW3193@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16052012-0008-0000-0000-000002A11CAD X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16052012-0009-0000-0000-00000D1B91C5 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-05-20_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_spam_policy_notspam policy=outbound_spam_policy score=0 spamscore=0 suspectscore=8 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1605200156 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 05/19/2016 05:10 PM, Peter Zijlstra wrote: > On Wed, May 18, 2016 at 11:11:51PM +0200, Rafael J. Wysocki wrote: >> On Wed, May 18, 2016 at 2:53 PM, Shilpasri G Bhat >> wrote: >>> This patch adds driver callback for fast_switch and below observations >>> on schedutil governor are done with this patch. >>> >>> In POWER8 there is a regression observed with schedutil compared to >>> ondemand. With schedutil the frequency is not ramping down and is >>> mostly stuck at max frequency during idle . This is because of the >>> watchdog timer, an RT task which is fired every 4 seconds which >>> results in requesting max frequency. >> >> Well, yes, that would be problematic. >> > > Right; we need to come up with something for RT tasks; but what happens > if you disable the watchdog? This should be entirely doable and might > give a better comparison. > Below are the comparisons by disabling watchdog. Both schedutil and ondemand have a similar ramp-down trend. And in both the cases I can see that frequency of the cpu is not reduced in deterministic fashion. In a observation window of 30 seconds after running a workload I can see that the frequency is not ramped down on some cpus in the system and are idling at max frequency. Below are the sample trace showcasing the frequency request when the cpu enters idle with schedutil. <...>-3528 7650.011010: cpu_frequency: state=4322000 cpu_id=120 <...>-3528 7650.027540: sched_switch: prev_comm=ppc64_cpu prev_state=x ==> next_comm=swapper/120 -0 7650.035017: cpu_frequency: state=4322000 cpu_id=120 -0 7729.683536: cpu_frequency: state=4322000 cpu_id=120 -0 7729.683552: sched_switch: prev_comm=swapper/120 prev_state=R ==> next_comm=kworker/120:1 kworker/120 7729.683565: sched_switch: prev_comm=kworker/120:1 prev_state=S ==> next_comm=swapper/120 However ondemand governor(with watchdog enabled) benefits from the noise created by watchdog timer and is able to brig down the frequency. Thanks and Regards, Shilpa