1// SPDX-License-Identifier: GPL-2.0
2/*
3 * haltpoll.c - haltpoll idle governor
4 *
5 * Copyright 2019 Red Hat, Inc. and/or its affiliates.
6 *
7 * This work is licensed under the terms of the GNU GPL, version 2. See
8 * the COPYING file in the top-level directory.
9 *
10 * Authors: Marcelo Tosatti <mtosatti@redhat.com>
11 */
12
13#include <linux/kernel.h>
14#include <linux/cpuidle.h>
15#include <linux/time.h>
16#include <linux/ktime.h>
17#include <linux/hrtimer.h>
18#include <linux/tick.h>
19#include <linux/sched.h>
20#include <linux/module.h>
21#include <linux/kvm_para.h>
22#include <trace/events/power.h>
23
24static unsigned int guest_halt_poll_ns __read_mostly = 200000;
25module_param(guest_halt_poll_ns, uint, 0644);
26
27/* division factor to shrink halt_poll_ns */
28static unsigned int guest_halt_poll_shrink __read_mostly = 2;
29module_param(guest_halt_poll_shrink, uint, 0644);
30
31/* multiplication factor to grow per-cpu poll_limit_ns */
32static unsigned int guest_halt_poll_grow __read_mostly = 2;
33module_param(guest_halt_poll_grow, uint, 0644);
34
35/* value in us to start growing per-cpu halt_poll_ns */
36static unsigned int guest_halt_poll_grow_start __read_mostly = 50000;
37module_param(guest_halt_poll_grow_start, uint, 0644);
38
39/* allow shrinking guest halt poll */
40static bool guest_halt_poll_allow_shrink __read_mostly = true;
41module_param(guest_halt_poll_allow_shrink, bool, 0644);
42
43/**
44 * haltpoll_select - selects the next idle state to enter
45 * @drv: cpuidle driver containing state data
46 * @dev: the CPU
47 * @stop_tick: indication on whether or not to stop the tick
48 */
49static int haltpoll_select(struct cpuidle_driver *drv,
50 struct cpuidle_device *dev,
51 bool *stop_tick)
52{
53 s64 latency_req = cpuidle_governor_latency_req(cpu: dev->cpu);
54
55 if (!drv->state_count || latency_req == 0) {
56 *stop_tick = false;
57 return 0;
58 }
59
60 if (dev->poll_limit_ns == 0)
61 return 1;
62
63 /* Last state was poll? */
64 if (dev->last_state_idx == 0) {
65 /* Halt if no event occurred on poll window */
66 if (dev->poll_time_limit == true)
67 return 1;
68
69 *stop_tick = false;
70 /* Otherwise, poll again */
71 return 0;
72 }
73
74 *stop_tick = false;
75 /* Last state was halt: poll */
76 return 0;
77}
78
79static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
80{
81 unsigned int val;
82
83 /* Grow cpu_halt_poll_us if
84 * cpu_halt_poll_us < block_ns < guest_halt_poll_us
85 */
86 if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) {
87 val = dev->poll_limit_ns * guest_halt_poll_grow;
88
89 if (val < guest_halt_poll_grow_start)
90 val = guest_halt_poll_grow_start;
91 if (val > guest_halt_poll_ns)
92 val = guest_halt_poll_ns;
93
94 trace_guest_halt_poll_ns_grow(val, dev->poll_limit_ns);
95 dev->poll_limit_ns = val;
96 } else if (block_ns > guest_halt_poll_ns &&
97 guest_halt_poll_allow_shrink) {
98 unsigned int shrink = guest_halt_poll_shrink;
99
100 val = dev->poll_limit_ns;
101 if (shrink == 0) {
102 val = 0;
103 } else {
104 val /= shrink;
105 /* Reset value to 0 if shrunk below grow_start */
106 if (val < guest_halt_poll_grow_start)
107 val = 0;
108 }
109
110 trace_guest_halt_poll_ns_shrink(val, dev->poll_limit_ns);
111 dev->poll_limit_ns = val;
112 }
113}
114
115/**
116 * haltpoll_reflect - update variables and update poll time
117 * @dev: the CPU
118 * @index: the index of actual entered state
119 */
120static void haltpoll_reflect(struct cpuidle_device *dev, int index)
121{
122 dev->last_state_idx = index;
123
124 if (index != 0)
125 adjust_poll_limit(dev, block_ns: dev->last_residency_ns);
126}
127
128/**
129 * haltpoll_enable_device - scans a CPU's states and does setup
130 * @drv: cpuidle driver
131 * @dev: the CPU
132 */
133static int haltpoll_enable_device(struct cpuidle_driver *drv,
134 struct cpuidle_device *dev)
135{
136 dev->poll_limit_ns = 0;
137
138 return 0;
139}
140
141static struct cpuidle_governor haltpoll_governor = {
142 .name = "haltpoll",
143 .rating = 9,
144 .enable = haltpoll_enable_device,
145 .select = haltpoll_select,
146 .reflect = haltpoll_reflect,
147};
148
149static int __init init_haltpoll(void)
150{
151 if (kvm_para_available())
152 return cpuidle_register_governor(gov: &haltpoll_governor);
153
154 return 0;
155}
156
157postcore_initcall(init_haltpoll);
158