softmmu/cpu-throttle.c

   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-common.h"
  27 #include "qemu/thread.h"
  28 #include "hw/core/cpu.h"
  29 #include "qemu/main-loop.h"
  30 #include "sysemu/cpus.h"
  31 #include "sysemu/cpu-throttle.h"
  32
  33 /* vcpu throttling controls */
  34 static QEMUTimer *throttle_timer;
  35 static unsigned int throttle_percentage;
  36
  37 #define CPU_THROTTLE_PCT_MIN 1
  38 #define CPU_THROTTLE_PCT_MAX 99
  39 #define CPU_THROTTLE_TIMESLICE_NS 10000000
  40
  41 static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque)
  42 {
  43     double pct;
  44     double throttle_ratio;
  45     int64_t sleeptime_ns, endtime_ns;
  46
  47     if (!cpu_throttle_get_percentage()) {
  48         return;
  49     }
  50
  51     pct = (double)cpu_throttle_get_percentage() / 100;
  52     throttle_ratio = pct / (1 - pct);
  53     /* Add 1ns to fix double's rounding error (like 0.9999999...) */
  54     sleeptime_ns = (int64_t)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS + 1);
  55     endtime_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + sleeptime_ns;
  56     while (sleeptime_ns > 0 && !cpu->stop) {
  57         if (sleeptime_ns > SCALE_MS) {
  58             qemu_cond_timedwait_iothread(cpu->halt_cond,
  59                                          sleeptime_ns / SCALE_MS);
  60         } else {
  61             qemu_mutex_unlock_iothread();
  62             g_usleep(sleeptime_ns / SCALE_US);
  63             qemu_mutex_lock_iothread();
  64         }
  65         sleeptime_ns = endtime_ns - qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
  66     }
  67     qatomic_set(&cpu->throttle_thread_scheduled, 0);
  68 }
  69
  70 static void cpu_throttle_timer_tick(void *opaque)
  71 {
  72     CPUState *cpu;
  73     double pct;
  74
  75     /* Stop the timer if needed */
  76     if (!cpu_throttle_get_percentage()) {
  77         return;
  78     }
  79     CPU_FOREACH(cpu) {
  80         if (!qatomic_xchg(&cpu->throttle_thread_scheduled, 1)) {
  81             async_run_on_cpu(cpu, cpu_throttle_thread,
  82                              RUN_ON_CPU_NULL);
  83         }
  84     }
  85
  86     pct = (double)cpu_throttle_get_percentage() / 100;
  87     timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +
  88                                    CPU_THROTTLE_TIMESLICE_NS / (1 - pct));
  89 }
  90
  91 void cpu_throttle_set(int new_throttle_pct)
  92 {
  93     /*
  94      * boolean to store whether throttle is already active or not,
  95      * before modifying throttle_percentage
  96      */
  97     bool throttle_active = cpu_throttle_active();
  98
  99     /* Ensure throttle percentage is within valid range */
 100     new_throttle_pct = MIN(new_throttle_pct, CPU_THROTTLE_PCT_MAX);
 101     new_throttle_pct = MAX(new_throttle_pct, CPU_THROTTLE_PCT_MIN);
 102
 103     qatomic_set(&throttle_percentage, new_throttle_pct);
 104
 105     if (!throttle_active) {
 106         cpu_throttle_timer_tick(NULL);
 107     }
 108 }
 109
 110 void cpu_throttle_stop(void)
 111 {
 112     qatomic_set(&throttle_percentage, 0);
 113 }
 114
 115 bool cpu_throttle_active(void)
 116 {
 117     return (cpu_throttle_get_percentage() != 0);
 118 }
 119
 120 int cpu_throttle_get_percentage(void)
 121 {
 122     return qatomic_read(&throttle_percentage);
 123 }
 124
 125 void cpu_throttle_init(void)
 126 {
 127     throttle_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,
 128                                   cpu_throttle_timer_tick, NULL);
 129 }