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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 4D2C8C31E4A for ; Thu, 13 Jun 2019 22:55:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E63F2147A for ; Thu, 13 Jun 2019 22:55:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727112AbfFMWzX (ORCPT ); Thu, 13 Jun 2019 18:55:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41638 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727136AbfFMWzP (ORCPT ); Thu, 13 Jun 2019 18:55:15 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 800288830C; Thu, 13 Jun 2019 22:55:15 +0000 (UTC) Received: from amt.cnet (ovpn-112-4.gru2.redhat.com [10.97.112.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id E8FC06085B; Thu, 13 Jun 2019 22:55:14 +0000 (UTC) Received: from amt.cnet (localhost [127.0.0.1]) by amt.cnet (Postfix) with ESMTP id 8B5AF105188; Thu, 13 Jun 2019 19:53:04 -0300 (BRT) Received: (from marcelo@localhost) by amt.cnet (8.14.7/8.14.7/Submit) id x5DMr4Kb025935; Thu, 13 Jun 2019 19:53:04 -0300 Message-ID: <20190613225023.011025297@redhat.com> User-Agent: quilt/0.66 Date: Thu, 13 Jun 2019 18:45:35 -0400 From: Marcelo Tosatti To: kvm-devel Cc: Paolo Bonzini , Radim Krcmar , Andrea Arcangeli , "Rafael J. Wysocki" , Peter Zijlstra , Wanpeng Li , Konrad Rzeszutek Wilk , Raslan KarimAllah , Boris Ostrovsky , Ankur Arora , Christian Borntraeger , linux-pm@vger.kernel.org, Marcelo Tosatti Subject: [patch 3/5] cpuidle: add haltpoll governor References: <20190613224532.949768676@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 13 Jun 2019 22:55:15 +0000 (UTC) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org The cpuidle_haltpoll governor, in conjunction with the haltpoll cpuidle driver, allows guest vcpus to poll for a specified amount of time before halting. This provides the following benefits to host side polling: 1) The POLL flag is set while polling is performed, which allows a remote vCPU to avoid sending an IPI (and the associated cost of handling the IPI) when performing a wakeup. 2) The VM-exit cost can be avoided. The downside of guest side polling is that polling is performed even with other runnable tasks in the host. Results comparing halt_poll_ns and server/client application where a small packet is ping-ponged: host --> 31.33 halt_poll_ns=300000 / no guest busy spin --> 33.40 (93.8%) halt_poll_ns=0 / guest_halt_poll_ns=300000 --> 32.73 (95.7%) For the SAP HANA benchmarks (where idle_spin is a parameter of the previous version of the patch, results should be the same): hpns == halt_poll_ns idle_spin=0/ idle_spin=800/ idle_spin=0/ hpns=200000 hpns=0 hpns=800000 DeleteC06T03 (100 thread) 1.76 1.71 (-3%) 1.78 (+1%) InsertC16T02 (100 thread) 2.14 2.07 (-3%) 2.18 (+1.8%) DeleteC00T01 (1 thread) 1.34 1.28 (-4.5%) 1.29 (-3.7%) UpdateC00T03 (1 thread) 4.72 4.18 (-12%) 4.53 (-5%) Signed-off-by: Marcelo Tosatti --- Documentation/virtual/guest-halt-polling.txt | 79 ++++++++++++ drivers/cpuidle/Kconfig | 11 + drivers/cpuidle/governors/Makefile | 1 drivers/cpuidle/governors/haltpoll.c | 175 +++++++++++++++++++++++++++ 4 files changed, 266 insertions(+) Index: linux-2.6.git/drivers/cpuidle/Kconfig =================================================================== --- linux-2.6.git.orig/drivers/cpuidle/Kconfig 2019-06-13 18:05:46.456294042 -0400 +++ linux-2.6.git/drivers/cpuidle/Kconfig 2019-06-13 18:14:58.981570277 -0400 @@ -33,6 +33,17 @@ Some workloads benefit from using it and it generally should be safe to use. Say Y here if you are not happy with the alternatives. +config CPU_IDLE_GOV_HALTPOLL + bool "Haltpoll governor (for virtualized systems)" + depends on KVM_GUEST + help + This governor implements haltpoll idle state selection, to be + used in conjunction with the haltpoll cpuidle driver, allowing + for polling for a certain amount of time before entering idle + state. + + Some virtualized workloads benefit from using it. + config DT_IDLE_STATES bool Index: linux-2.6.git/drivers/cpuidle/governors/Makefile =================================================================== --- linux-2.6.git.orig/drivers/cpuidle/governors/Makefile 2019-06-13 18:05:46.456294042 -0400 +++ linux-2.6.git/drivers/cpuidle/governors/Makefile 2019-06-13 18:10:53.861444033 -0400 @@ -6,3 +6,4 @@ obj-$(CONFIG_CPU_IDLE_GOV_LADDER) += ladder.o obj-$(CONFIG_CPU_IDLE_GOV_MENU) += menu.o obj-$(CONFIG_CPU_IDLE_GOV_TEO) += teo.o +obj-$(CONFIG_CPU_IDLE_GOV_HALTPOLL) += haltpoll.o Index: linux-2.6.git/drivers/cpuidle/governors/haltpoll.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-2.6.git/drivers/cpuidle/governors/haltpoll.c 2019-06-13 18:12:46.581615748 -0400 @@ -0,0 +1,175 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * haltpoll.c - haltpoll idle governor + * + * Copyright 2019 Red Hat, Inc. and/or its affiliates. + * + * This work is licensed under the terms of the GNU GPL, version 2. See + * the COPYING file in the top-level directory. + * + * Authors: Marcelo Tosatti + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +static unsigned int guest_halt_poll_us __read_mostly = 200; +module_param(guest_halt_poll_us, uint, 0644); + +/* division factor to shrink halt_poll_us */ +static unsigned int guest_halt_poll_shrink __read_mostly = 2; +module_param(guest_halt_poll_shrink, uint, 0644); + +/* multiplication factor to grow per-cpu halt_poll_us */ +static unsigned int guest_halt_poll_grow __read_mostly = 2; +module_param(guest_halt_poll_grow, uint, 0644); + +/* value in us to start growing per-cpu halt_poll_us */ +static unsigned int guest_halt_poll_grow_start __read_mostly = 50; +module_param(guest_halt_poll_grow_start, uint, 0644); + +/* allow shrinking guest halt poll */ +static bool guest_halt_poll_allow_shrink __read_mostly = true; +module_param(guest_halt_poll_allow_shrink, bool, 0644); + +struct haltpoll_device { + int last_state_idx; + unsigned int halt_poll_us; +}; + +static DEFINE_PER_CPU_ALIGNED(struct haltpoll_device, hpoll_devices); + +/** + * haltpoll_select - selects the next idle state to enter + * @drv: cpuidle driver containing state data + * @dev: the CPU + * @stop_tick: indication on whether or not to stop the tick + */ +static int haltpoll_select(struct cpuidle_driver *drv, + struct cpuidle_device *dev, + bool *stop_tick) +{ + struct haltpoll_device *hdev = this_cpu_ptr(&hpoll_devices); + + if (!drv->state_count) { + *stop_tick = false; + return 0; + } + + if (hdev->halt_poll_us == 0) + return 1; + + /* Last state was poll? */ + if (hdev->last_state_idx == 0) { + /* Halt if no event occurred on poll window */ + if (dev->poll_time_limit == true) + return 1; + + *stop_tick = false; + /* Otherwise, poll again */ + return 0; + } + + *stop_tick = false; + /* Last state was halt: poll */ + return 0; +} + +static void adjust_haltpoll_us(unsigned int block_us, + struct haltpoll_device *dev) +{ + unsigned int val; + + /* Grow cpu_halt_poll_us if + * cpu_halt_poll_us < block_ns < guest_halt_poll_us + */ + if (block_us > dev->halt_poll_us && block_us <= guest_halt_poll_us) { + val = dev->halt_poll_us * guest_halt_poll_grow; + + if (val < guest_halt_poll_grow_start) + val = guest_halt_poll_grow_start; + if (val > guest_halt_poll_us) + val = guest_halt_poll_us; + + dev->halt_poll_us = val; + } else if (block_us > guest_halt_poll_us && + guest_halt_poll_allow_shrink) { + unsigned int shrink = guest_halt_poll_shrink; + + val = dev->halt_poll_us; + if (shrink == 0) + val = 0; + else + val /= shrink; + dev->halt_poll_us = val; + } +} + +/** + * haltpoll_reflect - update variables and update poll time + * @dev: the CPU + * @index: the index of actual entered state + */ +static void haltpoll_reflect(struct cpuidle_device *dev, int index) +{ + struct haltpoll_device *hdev = this_cpu_ptr(&hpoll_devices); + + hdev->last_state_idx = index; + + if (index != 0) + adjust_haltpoll_us(dev->last_residency, hdev); +} + +/** + * haltpoll_enable_device - scans a CPU's states and does setup + * @drv: cpuidle driver + * @dev: the CPU + */ +static int haltpoll_enable_device(struct cpuidle_driver *drv, + struct cpuidle_device *dev) +{ + struct haltpoll_device *hdev = &per_cpu(hpoll_devices, dev->cpu); + + memset(hdev, 0, sizeof(struct haltpoll_device)); + + return 0; +} + +/** + * haltpoll_get_poll_time - return amount of poll time + * @drv: cpuidle driver + * @dev: the CPU + */ +static u64 haltpoll_get_poll_time(struct cpuidle_driver *drv, + struct cpuidle_device *dev) +{ + struct haltpoll_device *hdev = &per_cpu(hpoll_devices, dev->cpu); + + return hdev->halt_poll_us * NSEC_PER_USEC; +} + +static struct cpuidle_governor haltpoll_governor = { + .name = "haltpoll", + .rating = 21, + .enable = haltpoll_enable_device, + .select = haltpoll_select, + .reflect = haltpoll_reflect, + .get_poll_time = haltpoll_get_poll_time, +}; + +static int __init init_haltpoll(void) +{ + if (kvm_para_available()) + return cpuidle_register_governor(&haltpoll_governor); + + return 0; +} + +postcore_initcall(init_haltpoll); Index: linux-2.6.git/Documentation/virtual/guest-halt-polling.txt =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-2.6.git/Documentation/virtual/guest-halt-polling.txt 2019-06-13 18:16:22.414262777 -0400 @@ -0,0 +1,79 @@ +Guest halt polling +================== + +The cpuidle_haltpoll driver, with the haltpoll governor, allows +the guest vcpus to poll for a specified amount of time before +halting. +This provides the following benefits to host side polling: + + 1) The POLL flag is set while polling is performed, which allows + a remote vCPU to avoid sending an IPI (and the associated + cost of handling the IPI) when performing a wakeup. + + 2) The VM-exit cost can be avoided. + +The downside of guest side polling is that polling is performed +even with other runnable tasks in the host. + +The basic logic as follows: A global value, guest_halt_poll_us, +is configured by the user, indicating the maximum amount of +time polling is allowed. This value is fixed. + +Each vcpu has an adjustable guest_halt_poll_us +("per-cpu guest_halt_poll_us"), which is adjusted by the algorithm +in response to events (explained below). + +Module Parameters +================= + +The haltpoll governor has 5 tunable module parameters: + +1) guest_halt_poll_us: +Maximum amount of time, in microseconds, that polling is +performed before halting. + +Default: 200 + +2) guest_halt_poll_shrink: +Division factor used to shrink per-cpu guest_halt_poll_us when +wakeup event occurs after the global guest_halt_poll_us. + +Default: 2 + +3) guest_halt_poll_grow: +Multiplication factor used to grow per-cpu guest_halt_poll_us +when event occurs after per-cpu guest_halt_poll_us +but before global guest_halt_poll_us. + +Default: 2 + +4) guest_halt_poll_grow_start: +The per-cpu guest_halt_poll_us eventually reaches zero +in case of an idle system. This value sets the initial +per-cpu guest_halt_poll_us when growing. This can +be increased from 10, to avoid misses during the initial +growth stage: + +10, 20, 40, ... (example assumes guest_halt_poll_grow=2). + +Default: 50 + +5) guest_halt_poll_allow_shrink: + +Bool parameter which allows shrinking. Set to N +to avoid it (per-cpu guest_halt_poll_us will remain +high once achieves global guest_halt_poll_us value). + +Default: Y + +The module parameters can be set from the debugfs files in: + + /sys/module/haltpoll/parameters/ + +Further Notes +============= + +- Care should be taken when setting the guest_halt_poll_us parameter as a +large value has the potential to drive the cpu usage to 100% on a machine which +would be almost entirely idle otherwise. +