From patchwork Fri Jul 12 07:04:54 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Abhishek Goel X-Patchwork-Id: 11041621 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9200D912 for ; Fri, 12 Jul 2019 07:05:30 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8125828B5A for ; Fri, 12 Jul 2019 07:05:30 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 71D2F28BB9; Fri, 12 Jul 2019 07:05:30 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D8BCF28B5A for ; Fri, 12 Jul 2019 07:05:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725877AbfGLHF3 (ORCPT ); Fri, 12 Jul 2019 03:05:29 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:63390 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725840AbfGLHF3 (ORCPT ); Fri, 12 Jul 2019 03:05:29 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x6C73AMP075666 for ; Fri, 12 Jul 2019 03:05:27 -0400 Received: from e06smtp01.uk.ibm.com (e06smtp01.uk.ibm.com [195.75.94.97]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tpn2395rt-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 12 Jul 2019 03:05:27 -0400 Received: from localhost by e06smtp01.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, 12 Jul 2019 08:05:22 +0100 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x6C75Lax48693436 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 12 Jul 2019 07:05:21 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 255AA52052; Fri, 12 Jul 2019 07:05:21 +0000 (GMT) Received: from boston16h.aus.stglabs.ibm.com (unknown [9.3.23.78]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id A2FEC52054; Fri, 12 Jul 2019 07:05:19 +0000 (GMT) From: Abhishek Goel To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-pm@vger.kernel.org Cc: npiggin@gmail.com, rjw@rjwysocki.net, daniel.lezcano@linaro.org, mpe@ellerman.id.au, ego@linux.vnet.ibm.com, dja@axtens.net, Abhishek Goel Subject: [PATCH v4 0/3] Forced-wakeup for stop states on Powernv Date: Fri, 12 Jul 2019 02:04:54 -0500 X-Mailer: git-send-email 2.17.1 X-TM-AS-GCONF: 00 x-cbid: 19071207-4275-0000-0000-0000034C64FA X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19071207-4276-0000-0000-0000385C6E06 Message-Id: <20190712070457.55242-1-huntbag@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-07-12_02:,, 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=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1907120072 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 : 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 : Extended the forced wakeup logic for all states. Setting the decrementer instead of queuing up a hrtimer to implement the logic. v3 : 1) Cleanly handle setting the decrementer after exiting out of stop states. 2) Added a disable_callback feature to compute timeout whenever a state is enbaled or disabled instead of computing everytime in fast idle path. 3) Use disable callback to recompute timeout whenever state usage is changed for a state. Also, cleaned up the get_snooze_timeout function. v4 : Changed the type and name of set/reset decrementer function. Handled irq work pending in try_set_dec_before_idle. No change in patch 2 and 3. Abhishek Goel (3): cpuidle-powernv : forced wakeup for stop states cpuidle : Add callback whenever a state usage is enabled/disabled cpuidle-powernv : Recompute the idle-state timeouts when state usage is enabled/disabled arch/powerpc/include/asm/time.h | 2 ++ arch/powerpc/kernel/time.c | 43 ++++++++++++++++++++++++ drivers/cpuidle/cpuidle-powernv.c | 55 +++++++++++++++++++++++-------- drivers/cpuidle/sysfs.c | 15 ++++++++- include/linux/cpuidle.h | 5 +++ 5 files changed, 106 insertions(+), 14 deletions(-)