[v2,6/6] contrib/plugins: add ips plugin example for cost modeling

diff --git a/contrib/plugins/ips.c b/contrib/plugins/ips.c
new file mode 100644
index 00000000000..cf3159df391
--- /dev/null
+++ b/contrib/plugins/ips.c
@@ -0,0 +1,239 @@ 
+/*
+ * ips rate limiting plugin.
+ *
+ * This plugin can be used to restrict the execution of a system to a
+ * particular number of Instructions Per Second (ips). This controls
+ * time as seen by the guest so while wall-clock time may be longer
+ * from the guests point of view time will pass at the normal rate.
+ *
+ * This uses the new plugin API which allows the plugin to control
+ * system time.
+ *
+ * Copyright (c) 2023 Linaro Ltd
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <stdio.h>
+#include <glib.h>
+#include <qemu-plugin.h>
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
+
+/* how many times do we update time per sec */
+#define NUM_TIME_UPDATE_PER_SEC 10
+#define NSEC_IN_ONE_SEC (1000 * 1000 * 1000)
+
+static GMutex global_state_lock;
+
+static uint64_t insn_per_second = 1000 * 1000; /* ips per core, per second */
+static uint64_t insn_quantum; /* trap every N instructions */
+static bool precise_execution; /* count every instruction */
+static int64_t start_time_ns; /* time (ns since epoch) first vCPU started */
+static int64_t virtual_time_ns; /* last set virtual time */
+
+static const void *time_handle;
+
+typedef enum {
+    UNKNOWN = 0,
+    EXECUTING,
+    IDLE,
+    FINISHED
+} vCPUState;
+
+typedef struct {
+    uint64_t counter;
+    uint64_t track_insn;
+    vCPUState state;
+    /* timestamp when vCPU entered state */
+    int64_t last_state_time;
+} vCPUTime;
+
+struct qemu_plugin_scoreboard *vcpus;
+
+/* return epoch time in ns */
+static int64_t now_ns(void)
+{
+    return g_get_real_time() * 1000;
+}
+
+static uint64_t num_insn_during(int64_t elapsed_ns)
+{
+    double num_secs = elapsed_ns / (double) NSEC_IN_ONE_SEC;
+    return num_secs * (double) insn_per_second;
+}
+
+static int64_t time_for_insn(uint64_t num_insn)
+{
+    double num_secs = (double) num_insn / (double) insn_per_second;
+    return num_secs * (double) NSEC_IN_ONE_SEC;
+}
+
+static int64_t uptime_ns(void)
+{
+    int64_t now = now_ns();
+    g_assert(now >= start_time_ns);
+    return now - start_time_ns;
+}
+
+static void vcpu_set_state(vCPUTime *vcpu, vCPUState new_state)
+{
+    vcpu->last_state_time = now_ns();
+    vcpu->state = new_state;
+}
+
+static void update_system_time(vCPUTime *vcpu)
+{
+    /* flush remaining instructions */
+    vcpu->counter += vcpu->track_insn;
+    vcpu->track_insn = 0;
+
+    int64_t uptime = uptime_ns();
+    uint64_t expected_insn = num_insn_during(uptime);
+
+    if (vcpu->counter >= expected_insn) {
+        /* this vcpu ran faster than expected, so it has to sleep */
+        uint64_t insn_advance = vcpu->counter - expected_insn;
+        uint64_t time_advance_ns = time_for_insn(insn_advance);
+        int64_t sleep_us = time_advance_ns / 1000;
+        g_usleep(sleep_us);
+    }
+
+    /* based on number of instructions, what should be the new time? */
+    int64_t new_virtual_time = time_for_insn(vcpu->counter);
+
+    g_mutex_lock(&global_state_lock);
+
+    /* Time only moves forward. Another vcpu might have updated it already. */
+    if (new_virtual_time > virtual_time_ns) {
+        qemu_plugin_update_ns(time_handle, new_virtual_time);
+        virtual_time_ns = new_virtual_time;
+    }
+
+    g_mutex_unlock(&global_state_lock);
+}
+
+static void set_start_time()
+{
+    g_mutex_lock(&global_state_lock);
+    if (!start_time_ns) {
+        start_time_ns = now_ns();
+    }
+    g_mutex_unlock(&global_state_lock);
+}
+
+static void vcpu_init(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    /* ensure start time is set first */
+    set_start_time();
+    /* start counter from absolute time reference */
+    vcpu->counter = num_insn_during(uptime_ns());
+    vcpu_set_state(vcpu, EXECUTING);
+}
+
+static void vcpu_idle(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    vcpu_set_state(vcpu, IDLE);
+}
+
+static void vcpu_resume(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    g_assert(vcpu->state == IDLE);
+    int64_t idle_time = now_ns() - vcpu->last_state_time;
+    /* accumulate expected number of instructions */
+    vcpu->counter += num_insn_during(idle_time);
+    vcpu_set_state(vcpu, EXECUTING);
+}
+
+static void vcpu_exit(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    vcpu_set_state(vcpu, FINISHED);
+    update_system_time(vcpu);
+    vcpu->counter = 0;
+}
+
+static void every_insn_quantum(unsigned int cpu_index, void *udata)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    g_assert(vcpu->track_insn >= insn_quantum);
+    update_system_time(vcpu);
+}
+
+static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
+{
+    size_t n_insns = qemu_plugin_tb_n_insns(tb);
+    qemu_plugin_u64 track_insn =
+        qemu_plugin_scoreboard_u64_in_struct(vcpus, vCPUTime, track_insn);
+    if (precise_execution) {
+        /* count (and eventually trap) on every instruction */
+        for (int idx = 0; idx < qemu_plugin_tb_n_insns(tb); ++idx) {
+            struct qemu_plugin_insn *insn = qemu_plugin_tb_get_insn(tb, idx);
+            qemu_plugin_register_vcpu_insn_exec_inline_per_vcpu(
+                insn, QEMU_PLUGIN_INLINE_ADD_U64, track_insn, 1);
+            qemu_plugin_register_vcpu_insn_exec_cond_cb(
+                insn, every_insn_quantum,
+                QEMU_PLUGIN_CB_NO_REGS, QEMU_PLUGIN_COND_GE,
+                track_insn, insn_quantum, NULL);
+        }
+    } else {
+        /* count (and eventually trap) once per tb */
+        qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu(
+            tb, QEMU_PLUGIN_INLINE_ADD_U64, track_insn, n_insns);
+        qemu_plugin_register_vcpu_tb_exec_cond_cb(
+            tb, every_insn_quantum,
+            QEMU_PLUGIN_CB_NO_REGS, QEMU_PLUGIN_COND_GE,
+            track_insn, insn_quantum, NULL);
+    }
+}
+
+static void plugin_exit(qemu_plugin_id_t id, void *udata)
+{
+    qemu_plugin_scoreboard_free(vcpus);
+}
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
+                                           const qemu_info_t *info, int argc,
+                                           char **argv)
+{
+    for (int i = 0; i < argc; i++) {
+        char *opt = argv[i];
+        g_auto(GStrv) tokens = g_strsplit(opt, "=", 2);
+        if (g_strcmp0(tokens[0], "ips") == 0) {
+            insn_per_second = g_ascii_strtoull(tokens[1], NULL, 10);
+            if (!insn_per_second && errno) {
+                fprintf(stderr, "%s: couldn't parse %s (%s)\n",
+                        __func__, tokens[1], g_strerror(errno));
+                return -1;
+            }
+
+        } else if (g_strcmp0(tokens[0], "precise") == 0) {
+            if (!qemu_plugin_bool_parse(tokens[0], tokens[1],
+                                        &precise_execution)) {
+                fprintf(stderr, "boolean argument parsing failed: %s\n", opt);
+                return -1;
+            }
+        } else {
+            fprintf(stderr, "option parsing failed: %s\n", opt);
+            return -1;
+        }
+    }
+
+    vcpus = qemu_plugin_scoreboard_new(sizeof(vCPUTime));
+    insn_quantum = insn_per_second / NUM_TIME_UPDATE_PER_SEC;
+
+    time_handle = qemu_plugin_request_time_control();
+    g_assert(time_handle);
+
+    qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
+    qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
+    qemu_plugin_register_vcpu_idle_cb(id, vcpu_idle);
+    qemu_plugin_register_vcpu_resume_cb(id, vcpu_resume);
+    qemu_plugin_register_vcpu_exit_cb(id, vcpu_exit);
+    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
+
+    return 0;
+}
diff --git a/contrib/plugins/Makefile b/contrib/plugins/Makefile
index 0b64d2c1e3a..449ead11305 100644
--- a/contrib/plugins/Makefile
+++ b/contrib/plugins/Makefile
@@ -27,6 +27,7 @@  endif
 NAMES += hwprofile
 NAMES += cache
 NAMES += drcov
+NAMES += ips
 
 ifeq ($(CONFIG_WIN32),y)
 SO_SUFFIX := .dll