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  */
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 
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  */
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  */
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 
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