From patchwork Sun Apr 4 08:33:52 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Pratik R. Sampat" X-Patchwork-Id: 12182235 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=-11.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 D8D30C433ED for ; Sun, 4 Apr 2021 08:34:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B20516137F for ; Sun, 4 Apr 2021 08:34:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229950AbhDDIeN (ORCPT ); Sun, 4 Apr 2021 04:34:13 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:3134 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229861AbhDDIeN (ORCPT ); Sun, 4 Apr 2021 04:34:13 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 1348XgBK074889; Sun, 4 Apr 2021 04:34:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=from : to : subject : date : message-id : content-transfer-encoding : mime-version; s=pp1; bh=OHi2vwctu5KRILp+KYAuShu5xxEofmX7L+tcwpSherQ=; b=QxJe5/a2eGvqulK4X8FH0znoVN+vMnZj9YiQYpLGt8Jzbeq5c7cXi00BXL3dffwPeJF8 tPJeU0th0Va+9KAsIw+zENPr/cz7OkgJzRLvYU2C6ove1K9NbH5MfN/77TOlm7rFuRpr oymPAGMmjarJgNEFYf3+CH1ndhajXnFEtapFMFn/bTBr3ZzKY9zIlUjnKMNd/v/61ilZ i1Hu5OHF7n8kRt058ya7coEkw40XPe31KeRBS0NqFU6U7toUCjg68OOmI8rMLvaT4QW2 DxdFjpcbghM6JlafISam1ZCf0YpjHR4xHFos/QDbvU9yUeaps3RSU+kVRQ5IT+j/jRuI 6A== Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 37q5bx4m71-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sun, 04 Apr 2021 04:34:04 -0400 Received: from m0098410.ppops.net (m0098410.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.43/8.16.0.43) with SMTP id 1348Y39q075977; Sun, 4 Apr 2021 04:34:03 -0400 Received: from ppma03ams.nl.ibm.com (62.31.33a9.ip4.static.sl-reverse.com [169.51.49.98]) by mx0a-001b2d01.pphosted.com with ESMTP id 37q5bx4m6g-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sun, 04 Apr 2021 04:34:03 -0400 Received: from pps.filterd (ppma03ams.nl.ibm.com [127.0.0.1]) by ppma03ams.nl.ibm.com (8.16.0.43/8.16.0.43) with SMTP id 1348Xggb000725; Sun, 4 Apr 2021 08:34:01 GMT Received: from b06cxnps3074.portsmouth.uk.ibm.com (d06relay09.portsmouth.uk.ibm.com [9.149.109.194]) by ppma03ams.nl.ibm.com with ESMTP id 37q2y9g7hg-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sun, 04 Apr 2021 08:34:01 +0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 1348Xw1Q22938088 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sun, 4 Apr 2021 08:33:58 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2FB084C040; Sun, 4 Apr 2021 08:33:58 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9A32F4C044; Sun, 4 Apr 2021 08:33:55 +0000 (GMT) Received: from pratiks-thinkpad.ibmuc.com (unknown [9.85.90.174]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Sun, 4 Apr 2021 08:33:55 +0000 (GMT) From: Pratik Rajesh Sampat To: rjw@rjwysocki.net, daniel.lezcano@linaro.org, shuah@kernel.org, dsmythies@telus.net, ego@linux.vnet.ibm.com, svaidy@linux.ibm.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, pratik.r.sampat@gmail.com, psampat@linux.ibm.com Subject: [RFC v3 0/2] CPU-Idle latency selftest framework Date: Sun, 4 Apr 2021 14:03:52 +0530 Message-Id: <20210404083354.23060-1-psampat@linux.ibm.com> X-Mailer: git-send-email 2.30.2 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: M2wbZFKqMMmK2AqBxP7D4A6Xy34zCsvN X-Proofpoint-ORIG-GUID: _FWaEj3xlXnVbkWZmODaSf403vnSq3Oc X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-04-04_01:2021-04-01,2021-04-04 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 mlxlogscore=999 priorityscore=1501 mlxscore=0 malwarescore=0 lowpriorityscore=0 adultscore=0 phishscore=0 bulkscore=0 suspectscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104030000 definitions=main-2104040058 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Changelog RFC v2-->v3 Based on comments by Doug Smythies, 1. Changed commit log to reflect the test must be run as super user. 2. Added a comment specifying a method to run the test bash script without recompiling. 3. Enable all the idle states after the experiments are completed so that the system is in a coherent state after the tests have run 4. Correct the return status of a CPU that cannot be off-lined. RFC v2: https://lkml.org/lkml/2021/4/1/615 --- A kernel module + userspace driver to estimate the wakeup latency caused by going into stop states. The motivation behind this program is to find significant deviations behind advertised latency and residency values. The patchset measures latencies for two kinds of events. IPIs and Timers As this is a software-only mechanism, there will additional latencies of the kernel-firmware-hardware interactions. To account for that, the program also measures a baseline latency on a 100 percent loaded CPU and the latencies achieved must be in view relative to that. To achieve this, we introduce a kernel module and expose its control knobs through the debugfs interface that the selftests can engage with. The kernel module provides the following interfaces within /sys/kernel/debug/latency_test/ for, IPI test: ipi_cpu_dest = Destination CPU for the IPI ipi_cpu_src = Origin of the IPI ipi_latency_ns = Measured latency time in ns Timeout test: timeout_cpu_src = CPU on which the timer to be queued timeout_expected_ns = Timer duration timeout_diff_ns = Difference of actual duration vs expected timer Sample output on a POWER9 system is as follows: # --IPI Latency Test--- # Baseline Average IPI latency(ns): 3114 # Observed Average IPI latency(ns) - State0: 3265 # Observed Average IPI latency(ns) - State1: 3507 # Observed Average IPI latency(ns) - State2: 3739 # Observed Average IPI latency(ns) - State3: 3807 # Observed Average IPI latency(ns) - State4: 17070 # Observed Average IPI latency(ns) - State5: 1038174 # Observed Average IPI latency(ns) - State6: 1068784 # # --Timeout Latency Test-- # Baseline Average timeout diff(ns): 1420 # Observed Average timeout diff(ns) - State0: 1640 # Observed Average timeout diff(ns) - State1: 1764 # Observed Average timeout diff(ns) - State2: 1715 # Observed Average timeout diff(ns) - State3: 1845 # Observed Average timeout diff(ns) - State4: 16581 # Observed Average timeout diff(ns) - State5: 939977 # Observed Average timeout diff(ns) - State6: 1073024 Things to keep in mind: 1. This kernel module + bash driver does not guarantee idleness on a core when the IPI and the Timer is armed. It only invokes sleep and hopes that the core is idle once the IPI/Timer is invoked onto it. Hence this program must be run on a completely idle system for best results 2. Even on a completely idle system, there maybe book-keeping tasks or jitter tasks that can run on the core we want idle. This can create outliers in the latency measurement. Thankfully, these outliers should be large enough to easily weed them out. 3. A userspace only selftest variant was also sent out as RFC based on suggestions over the previous patchset to simply the kernel complexeity. However, a userspace only approach had more noise in the latency measurement due to userspace-kernel interactions which led to run to run variance and a lesser accurate test. Another downside of the nature of a userspace program is that it takes orders of magnitude longer to complete a full system test compared to the kernel framework. RFC patch: https://lkml.org/lkml/2020/9/2/356 4. For Intel Systems, the Timer based latencies don't exactly give out the measure of idle latencies. This is because of a hardware optimization mechanism that pre-arms a CPU when a timer is set to wakeup. That doesn't make this metric useless for Intel systems, it just means that is measuring IPI/Timer responding latency rather than idle wakeup latencies. (Source: https://lkml.org/lkml/2020/9/2/610) For solution to this problem, a hardware based latency analyzer is devised by Artem Bityutskiy from Intel. https://youtu.be/Opk92aQyvt0?t=8266 https://intel.github.io/wult/ Pratik Rajesh Sampat (2): cpuidle: Extract IPI based and timer based wakeup latency from idle states selftest/cpuidle: Add support for cpuidle latency measurement drivers/cpuidle/Makefile | 1 + drivers/cpuidle/test-cpuidle_latency.c | 157 ++++++++++ lib/Kconfig.debug | 10 + tools/testing/selftests/Makefile | 1 + tools/testing/selftests/cpuidle/Makefile | 6 + tools/testing/selftests/cpuidle/cpuidle.sh | 326 +++++++++++++++++++++ tools/testing/selftests/cpuidle/settings | 2 + 7 files changed, 503 insertions(+) create mode 100644 drivers/cpuidle/test-cpuidle_latency.c create mode 100644 tools/testing/selftests/cpuidle/Makefile create mode 100755 tools/testing/selftests/cpuidle/cpuidle.sh create mode 100644 tools/testing/selftests/cpuidle/settings