system/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/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
  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
  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
  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
 109 void cpu_throttle_stop(void)
 110 {
 111     qatomic_set(&throttle_percentage, 0);
 112 }
 113
 114 bool cpu_throttle_active(void)
 115 {
 116     return (cpu_throttle_get_percentage() != 0);
 117 }
 118
 119 int cpu_throttle_get_percentage(void)
 120 {
 121     return qatomic_read(&throttle_percentage);
 122 }
 123
 124 void cpu_throttle_init(void)
 125 {
 126     throttle_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,
 127                                   cpu_throttle_timer_tick, NULL);
 128 }