1 /* 2 * Instructions Per Second (IPS) rate limiting plugin. 3 * 4 * This plugin can be used to restrict the execution of a system to a 5 * particular number of Instructions Per Second (IPS). This controls 6 * time as seen by the guest so while wall-clock time may be longer 7 * from the guests point of view time will pass at the normal rate. 8 * 9 * This uses the new plugin API which allows the plugin to control 10 * system time. 11 * 12 * Copyright (c) 2023 Linaro Ltd 13 * 14 * SPDX-License-Identifier: GPL-2.0-or-later 15 */ 16 17 #include <stdio.h> 18 #include <glib.h> 19 #include <qemu-plugin.h> 20 21 QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION; 22 23 /* how many times do we update time per sec */ 24 #define NUM_TIME_UPDATE_PER_SEC 10 25 #define NSEC_IN_ONE_SEC (1000 * 1000 * 1000) 26 27 static GMutex global_state_lock; 28 29 static uint64_t max_insn_per_second = 1000 * 1000 * 1000; /* ips per core, per second */ 30 static uint64_t max_insn_per_quantum; /* trap every N instructions */ 31 static int64_t virtual_time_ns; /* last set virtual time */ 32 33 static const void *time_handle; 34 35 typedef struct { 36 uint64_t total_insn; 37 uint64_t quantum_insn; /* insn in last quantum */ 38 int64_t last_quantum_time; /* time when last quantum started */ 39 } vCPUTime; 40 41 struct qemu_plugin_scoreboard *vcpus; 42 43 /* return epoch time in ns */ 44 static int64_t now_ns(void) 45 { 46 return g_get_real_time() * 1000; 47 } 48 49 static uint64_t num_insn_during(int64_t elapsed_ns) 50 { 51 double num_secs = elapsed_ns / (double) NSEC_IN_ONE_SEC; 52 return num_secs * (double) max_insn_per_second; 53 } 54 55 static int64_t time_for_insn(uint64_t num_insn) 56 { 57 double num_secs = (double) num_insn / (double) max_insn_per_second; 58 return num_secs * (double) NSEC_IN_ONE_SEC; 59 } 60 61 static void update_system_time(vCPUTime *vcpu) 62 { 63 int64_t elapsed_ns = now_ns() - vcpu->last_quantum_time; 64 uint64_t max_insn = num_insn_during(elapsed_ns); 65 66 if (vcpu->quantum_insn >= max_insn) { 67 /* this vcpu ran faster than expected, so it has to sleep */ 68 uint64_t insn_advance = vcpu->quantum_insn - max_insn; 69 uint64_t time_advance_ns = time_for_insn(insn_advance); 70 int64_t sleep_us = time_advance_ns / 1000; 71 g_usleep(sleep_us); 72 } 73 74 vcpu->total_insn += vcpu->quantum_insn; 75 vcpu->quantum_insn = 0; 76 vcpu->last_quantum_time = now_ns(); 77 78 /* based on total number of instructions, what should be the new time? */ 79 int64_t new_virtual_time = time_for_insn(vcpu->total_insn); 80 81 g_mutex_lock(&global_state_lock); 82 83 /* Time only moves forward. Another vcpu might have updated it already. */ 84 if (new_virtual_time > virtual_time_ns) { 85 qemu_plugin_update_ns(time_handle, new_virtual_time); 86 virtual_time_ns = new_virtual_time; 87 } 88 89 g_mutex_unlock(&global_state_lock); 90 } 91 92 static void vcpu_init(qemu_plugin_id_t id, unsigned int cpu_index) 93 { 94 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index); 95 vcpu->total_insn = 0; 96 vcpu->quantum_insn = 0; 97 vcpu->last_quantum_time = now_ns(); 98 } 99 100 static void vcpu_exit(qemu_plugin_id_t id, unsigned int cpu_index) 101 { 102 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index); 103 update_system_time(vcpu); 104 } 105 106 static void every_quantum_insn(unsigned int cpu_index, void *udata) 107 { 108 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index); 109 g_assert(vcpu->quantum_insn >= max_insn_per_quantum); 110 update_system_time(vcpu); 111 } 112 113 static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb) 114 { 115 size_t n_insns = qemu_plugin_tb_n_insns(tb); 116 qemu_plugin_u64 quantum_insn = 117 qemu_plugin_scoreboard_u64_in_struct(vcpus, vCPUTime, quantum_insn); 118 /* count (and eventually trap) once per tb */ 119 qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu( 120 tb, QEMU_PLUGIN_INLINE_ADD_U64, quantum_insn, n_insns); 121 qemu_plugin_register_vcpu_tb_exec_cond_cb( 122 tb, every_quantum_insn, 123 QEMU_PLUGIN_CB_NO_REGS, QEMU_PLUGIN_COND_GE, 124 quantum_insn, max_insn_per_quantum, NULL); 125 } 126 127 static void plugin_exit(qemu_plugin_id_t id, void *udata) 128 { 129 qemu_plugin_scoreboard_free(vcpus); 130 } 131 132 QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id, 133 const qemu_info_t *info, int argc, 134 char **argv) 135 { 136 for (int i = 0; i < argc; i++) { 137 char *opt = argv[i]; 138 g_auto(GStrv) tokens = g_strsplit(opt, "=", 2); 139 if (g_strcmp0(tokens[0], "ips") == 0) { 140 max_insn_per_second = g_ascii_strtoull(tokens[1], NULL, 10); 141 if (!max_insn_per_second && errno) { 142 fprintf(stderr, "%s: couldn't parse %s (%s)\n", 143 __func__, tokens[1], g_strerror(errno)); 144 return -1; 145 } 146 } else { 147 fprintf(stderr, "option parsing failed: %s\n", opt); 148 return -1; 149 } 150 } 151 152 vcpus = qemu_plugin_scoreboard_new(sizeof(vCPUTime)); 153 max_insn_per_quantum = max_insn_per_second / NUM_TIME_UPDATE_PER_SEC; 154 155 if (max_insn_per_quantum == 0) { 156 fprintf(stderr, "minimum of %d instructions per second needed\n", 157 NUM_TIME_UPDATE_PER_SEC); 158 return -1; 159 } 160 161 time_handle = qemu_plugin_request_time_control(); 162 g_assert(time_handle); 163 164 qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans); 165 qemu_plugin_register_vcpu_init_cb(id, vcpu_init); 166 qemu_plugin_register_vcpu_exit_cb(id, vcpu_exit); 167 qemu_plugin_register_atexit_cb(id, plugin_exit, NULL); 168 169 return 0; 170 } 171