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 	int 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, unsigned int block_us)
79 {
80 	unsigned int val;
81 	u64 block_ns = block_us*NSEC_PER_USEC;
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 		dev->poll_limit_ns = val;
95 	} else if (block_ns > guest_halt_poll_ns &&
96 		   guest_halt_poll_allow_shrink) {
97 		unsigned int shrink = guest_halt_poll_shrink;
98 
99 		val = dev->poll_limit_ns;
100 		if (shrink == 0)
101 			val = 0;
102 		else
103 			val /= shrink;
104 		dev->poll_limit_ns = val;
105 	}
106 }
107 
108 /**
109  * haltpoll_reflect - update variables and update poll time
110  * @dev: the CPU
111  * @index: the index of actual entered state
112  */
113 static void haltpoll_reflect(struct cpuidle_device *dev, int index)
114 {
115 	dev->last_state_idx = index;
116 
117 	if (index != 0)
118 		adjust_poll_limit(dev, dev->last_residency);
119 }
120 
121 /**
122  * haltpoll_enable_device - scans a CPU's states and does setup
123  * @drv: cpuidle driver
124  * @dev: the CPU
125  */
126 static int haltpoll_enable_device(struct cpuidle_driver *drv,
127 				  struct cpuidle_device *dev)
128 {
129 	dev->poll_limit_ns = 0;
130 
131 	return 0;
132 }
133 
134 static struct cpuidle_governor haltpoll_governor = {
135 	.name =			"haltpoll",
136 	.rating =		9,
137 	.enable =		haltpoll_enable_device,
138 	.select =		haltpoll_select,
139 	.reflect =		haltpoll_reflect,
140 };
141 
142 static int __init init_haltpoll(void)
143 {
144 	if (kvm_para_available())
145 		return cpuidle_register_governor(&haltpoll_governor);
146 
147 	return 0;
148 }
149 
150 postcore_initcall(init_haltpoll);
151