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
23 static unsigned int guest_halt_poll_ns __read_mostly = 200000;
24 module_param(guest_halt_poll_ns, uint, 0644);
25
26 /* division factor to shrink halt_poll_ns */
27 static unsigned int guest_halt_poll_shrink __read_mostly = 2;
28 module_param(guest_halt_poll_shrink, uint, 0644);
29
30 /* multiplication factor to grow per-cpu poll_limit_ns */
31 static unsigned int guest_halt_poll_grow __read_mostly = 2;
32 module_param(guest_halt_poll_grow, uint, 0644);
33
34 /* value in us to start growing per-cpu halt_poll_ns */
35 static unsigned int guest_halt_poll_grow_start __read_mostly = 50000;
36 module_param(guest_halt_poll_grow_start, uint, 0644);
37
38 /* allow shrinking guest halt poll */
39 static bool guest_halt_poll_allow_shrink __read_mostly = true;
40 module_param(guest_halt_poll_allow_shrink, bool, 0644);
41
42 /**
43 * haltpoll_select - selects the next idle state to enter
44 * @drv: cpuidle driver containing state data
45 * @dev: the CPU
46 * @stop_tick: indication on whether or not to stop the tick
47 */
haltpoll_select(struct cpuidle_driver * drv,struct cpuidle_device * dev,bool * stop_tick)48 static int haltpoll_select(struct cpuidle_driver *drv,
49 struct cpuidle_device *dev,
50 bool *stop_tick)
51 {
52 s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
53
54 if (!drv->state_count || latency_req == 0) {
55 *stop_tick = false;
56 return 0;
57 }
58
59 if (dev->poll_limit_ns == 0)
60 return 1;
61
62 /* Last state was poll? */
63 if (dev->last_state_idx == 0) {
64 /* Halt if no event occurred on poll window */
65 if (dev->poll_time_limit == true)
66 return 1;
67
68 *stop_tick = false;
69 /* Otherwise, poll again */
70 return 0;
71 }
72
73 *stop_tick = false;
74 /* Last state was halt: poll */
75 return 0;
76 }
77
adjust_poll_limit(struct cpuidle_device * dev,u64 block_ns)78 static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
79 {
80 unsigned int val;
81
82 /* Grow cpu_halt_poll_us if
83 * cpu_halt_poll_us < block_ns < guest_halt_poll_us
84 */
85 if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) {
86 val = dev->poll_limit_ns * guest_halt_poll_grow;
87
88 if (val < guest_halt_poll_grow_start)
89 val = guest_halt_poll_grow_start;
90 if (val > guest_halt_poll_ns)
91 val = guest_halt_poll_ns;
92
93 dev->poll_limit_ns = val;
94 } else if (block_ns > guest_halt_poll_ns &&
95 guest_halt_poll_allow_shrink) {
96 unsigned int shrink = guest_halt_poll_shrink;
97
98 val = dev->poll_limit_ns;
99 if (shrink == 0)
100 val = 0;
101 else
102 val /= shrink;
103 dev->poll_limit_ns = val;
104 }
105 }
106
107 /**
108 * haltpoll_reflect - update variables and update poll time
109 * @dev: the CPU
110 * @index: the index of actual entered state
111 */
haltpoll_reflect(struct cpuidle_device * dev,int index)112 static void haltpoll_reflect(struct cpuidle_device *dev, int index)
113 {
114 dev->last_state_idx = index;
115
116 if (index != 0)
117 adjust_poll_limit(dev, dev->last_residency_ns);
118 }
119
120 /**
121 * haltpoll_enable_device - scans a CPU's states and does setup
122 * @drv: cpuidle driver
123 * @dev: the CPU
124 */
haltpoll_enable_device(struct cpuidle_driver * drv,struct cpuidle_device * dev)125 static int haltpoll_enable_device(struct cpuidle_driver *drv,
126 struct cpuidle_device *dev)
127 {
128 dev->poll_limit_ns = 0;
129
130 return 0;
131 }
132
133 static struct cpuidle_governor haltpoll_governor = {
134 .name = "haltpoll",
135 .rating = 9,
136 .enable = haltpoll_enable_device,
137 .select = haltpoll_select,
138 .reflect = haltpoll_reflect,
139 };
140
init_haltpoll(void)141 static int __init init_haltpoll(void)
142 {
143 if (kvm_para_available())
144 return cpuidle_register_governor(&haltpoll_governor);
145
146 return 0;
147 }
148
149 postcore_initcall(init_haltpoll);
150