xref: /openbmc/qemu/system/cpu-throttle.c (revision 7c754c78)
1 /*
2  * QEMU System Emulator
3  *
4  * Copyright (c) 2003-2008 Fabrice Bellard
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining a copy
7  * of this software and associated documentation files (the "Software"), to deal
8  * in the Software without restriction, including without limitation the rights
9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10  * copies of the Software, and to permit persons to whom the Software is
11  * furnished to do so, subject to the following conditions:
12  *
13  * The above copyright notice and this permission notice shall be included in
14  * all copies or substantial portions of the Software.
15  *
16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22  * THE SOFTWARE.
23  */
24 
25 #include "qemu/osdep.h"
26 #include "qemu/thread.h"
27 #include "hw/core/cpu.h"
28 #include "qemu/main-loop.h"
29 #include "sysemu/cpus.h"
30 #include "sysemu/cpu-throttle.h"
31 
32 /* vcpu throttling controls */
33 static QEMUTimer *throttle_timer;
34 static unsigned int throttle_percentage;
35 
36 #define CPU_THROTTLE_PCT_MIN 1
37 #define CPU_THROTTLE_PCT_MAX 99
38 #define CPU_THROTTLE_TIMESLICE_NS 10000000
39 
cpu_throttle_thread(CPUState * cpu,run_on_cpu_data opaque)40 static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque)
41 {
42     double pct;
43     double throttle_ratio;
44     int64_t sleeptime_ns, endtime_ns;
45 
46     if (!cpu_throttle_get_percentage()) {
47         return;
48     }
49 
50     pct = (double)cpu_throttle_get_percentage() / 100;
51     throttle_ratio = pct / (1 - pct);
52     /* Add 1ns to fix double's rounding error (like 0.9999999...) */
53     sleeptime_ns = (int64_t)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS + 1);
54     endtime_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + sleeptime_ns;
55     while (sleeptime_ns > 0 && !cpu->stop) {
56         if (sleeptime_ns > SCALE_MS) {
57             qemu_cond_timedwait_bql(cpu->halt_cond,
58                                          sleeptime_ns / SCALE_MS);
59         } else {
60             bql_unlock();
61             g_usleep(sleeptime_ns / SCALE_US);
62             bql_lock();
63         }
64         sleeptime_ns = endtime_ns - qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
65     }
66     qatomic_set(&cpu->throttle_thread_scheduled, 0);
67 }
68 
cpu_throttle_timer_tick(void * opaque)69 static void cpu_throttle_timer_tick(void *opaque)
70 {
71     CPUState *cpu;
72     double pct;
73 
74     /* Stop the timer if needed */
75     if (!cpu_throttle_get_percentage()) {
76         return;
77     }
78     CPU_FOREACH(cpu) {
79         if (!qatomic_xchg(&cpu->throttle_thread_scheduled, 1)) {
80             async_run_on_cpu(cpu, cpu_throttle_thread,
81                              RUN_ON_CPU_NULL);
82         }
83     }
84 
85     pct = (double)cpu_throttle_get_percentage() / 100;
86     timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +
87                                    CPU_THROTTLE_TIMESLICE_NS / (1 - pct));
88 }
89 
cpu_throttle_set(int new_throttle_pct)90 void cpu_throttle_set(int new_throttle_pct)
91 {
92     /*
93      * boolean to store whether throttle is already active or not,
94      * before modifying throttle_percentage
95      */
96     bool throttle_active = cpu_throttle_active();
97 
98     /* Ensure throttle percentage is within valid range */
99     new_throttle_pct = MIN(new_throttle_pct, CPU_THROTTLE_PCT_MAX);
100     new_throttle_pct = MAX(new_throttle_pct, CPU_THROTTLE_PCT_MIN);
101 
102     qatomic_set(&throttle_percentage, new_throttle_pct);
103 
104     if (!throttle_active) {
105         cpu_throttle_timer_tick(NULL);
106     }
107 }
108 
cpu_throttle_stop(void)109 void cpu_throttle_stop(void)
110 {
111     qatomic_set(&throttle_percentage, 0);
112 }
113 
cpu_throttle_active(void)114 bool cpu_throttle_active(void)
115 {
116     return (cpu_throttle_get_percentage() != 0);
117 }
118 
cpu_throttle_get_percentage(void)119 int cpu_throttle_get_percentage(void)
120 {
121     return qatomic_read(&throttle_percentage);
122 }
123 
cpu_throttle_init(void)124 void cpu_throttle_init(void)
125 {
126     throttle_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,
127                                   cpu_throttle_timer_tick, NULL);
128 }
129