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=-2.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 E30C3C31E57 for ; Mon, 17 Jun 2019 10:00:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C229320833 for ; Mon, 17 Jun 2019 10:00:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727646AbfFQKAc (ORCPT ); Mon, 17 Jun 2019 06:00:32 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:37238 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727545AbfFQKAc (ORCPT ); Mon, 17 Jun 2019 06:00:32 -0400 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5H9xdmF056996 for ; Mon, 17 Jun 2019 06:00:31 -0400 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0a-001b2d01.pphosted.com with ESMTP id 2t671tc5ty-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 17 Jun 2019 06:00:30 -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) Mon, 17 Jun 2019 11:00:24 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5HA0Nq642401928 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 17 Jun 2019 10:00:23 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 963AEA405D; Mon, 17 Jun 2019 10:00:23 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 27194A404D; Mon, 17 Jun 2019 10:00:22 +0000 (GMT) Received: from boston16h.aus.stglabs.ibm.com (unknown [9.3.23.78]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 17 Jun 2019 10:00:21 +0000 (GMT) From: Abhishek Goel To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-pm@vger.kernel.org Cc: rjw@rjwysocki.net, daniel.lezcano@linaro.org, mpe@ellerman.id.au, dja@axtens.net, npiggin@gmail.com, ego@linux.vnet.ibm.com, Abhishek Goel Subject: [PATCH v2 0/1] Forced-wakeup for stop states on Powernv Date: Mon, 17 Jun 2019 04:56:47 -0500 X-Mailer: git-send-email 2.17.1 X-TM-AS-GCONF: 00 x-cbid: 19061710-0012-0000-0000-00000329CB13 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19061710-0013-0000-0000-00002162E1DC Message-Id: <20190617095648.18847-1-huntbag@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-17_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=823 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906170093 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Currently, the cpuidle governors determine what idle state a idling CPU should enter into based on heuristics that depend on the idle history on that CPU. Given that no predictive heuristic is perfect, there are cases where the governor predicts a shallow idle state, hoping that the CPU will be busy soon. However, if no new workload is scheduled on that CPU in the near future, the CPU will end up in the shallow state. Motivation ---------- In case of POWER, this is problematic, when the predicted state in the aforementioned scenario is a shallow stop state on a tickless system. As we might get stuck into shallow states even for hours, in absence of ticks or interrupts. To address this, We forcefully wakeup the cpu by setting the decrementer. The decrementer is set to a value that corresponds with the residency of the next available state. Thus firing up a timer that will forcefully wakeup the cpu. Few such iterations will essentially train the governor to select a deeper state for that cpu, as the timer here corresponds to the next available cpuidle state residency. Thus, cpu will eventually end up in the deepest possible state and we won't get stuck in a shallow state for long duration. Experiment ---------- For earlier versions when this feature was meat to be only for shallow lite states, I performed experiments for three scenarios to collect some data. case 1 : Without this patch and without tick retained, i.e. in a upstream kernel, It would spend more than even a second to get out of stop0_lite. case 2 : With tick retained in a upstream kernel - Generally, we have a sched tick at 4ms(CONF_HZ = 250). Ideally I expected it to take 8 sched tick to get out of stop0_lite. Experimentally, observation was ========================================================= sample min max 99percentile 20 4ms 12ms 4ms ========================================================= It would take atleast one sched tick to get out of stop0_lite. case 2 : With this patch (not stopping tick, but explicitly queuing a timer) ============================================================ sample min max 99percentile ============================================================ 20 144us 192us 144us ============================================================ Description of current implementation ------------------------------------- We calculate timeout for the current idle state as the residency value of the next available idle state. If the decrementer is set to be greater than this timeout, we update the decrementer value with the residency of next available idle state. Thus, essentially training the governor to select the next available deeper state until we reach the deepest state. Hence, we won't get stuck unnecessarily in shallow states for longer duration. -------------------------------- v1 of auto-promotion : https://lkml.org/lkml/2019/3/22/58 This patch was implemented only for shallow lite state in generic cpuidle driver. v2 of auto-promotion : Removed timeout_needed and rebased to current upstream kernel Then, v1 of forced-wakeup : Moved the code to cpuidle powernv driver and started as forced wakeup instead of auto-promotion v2 of forced-wakeup : Extended the forced wakeup logic for all states. Setting the decrementer instead of queuing up a hrtimer to implement the logic. Abhishek Goel (1): cpuidle-powernv : forced wakeup for stop states drivers/cpuidle/cpuidle-powernv.c | 38 +++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) -- 2.17.1