Examples
--------
Slow down execution of /bin/true:
$ num_insn=$(./build/qemu-x86_64 -plugin ./build/tests/plugin/libinsn.so -d plugin /bin/true |& grep total | sed -e 's/.*: //')
$ time ./build/qemu-x86_64 -plugin ./build/contrib/plugins/libips.so,ips=$(($num_insn/4)) /bin/true
real 4.000s
Boot a Linux kernel simulating a 250MHz cpu:
$ /build/qemu-system-x86_64 -kernel /boot/vmlinuz-6.1.0-21-amd64 -append "console=ttyS0" -plugin ./build/contrib/plugins/libips.so,ips=$((250*1000*1000)) -smp 1 -m 512
check time until kernel panic on serial0
Tested in system mode by booting a full debian system, and using:
$ sysbench cpu run
Performance decrease linearly with the given number of ips.
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@xxxxxxxxxx>
Message-Id: <20240530220610.1245424-7-pierrick.bouvier@xxxxxxxxxx>
---
contrib/plugins/ips.c | 164 +++++++++++++++++++++++++++++++++++++++
contrib/plugins/Makefile | 1 +
2 files changed, 165 insertions(+)
create mode 100644 contrib/plugins/ips.c
diff --git a/contrib/plugins/ips.c b/contrib/plugins/ips.c
new file mode 100644
index 0000000000..db77729264
--- /dev/null
+++ b/contrib/plugins/ips.c
@@ -0,0 +1,164 @@
+/*
+ * 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 max_insn_per_second = 1000 * 1000 * 1000; /* ips per core, per second */
+static uint64_t max_insn_per_quantum; /* trap every N instructions */
+static int64_t virtual_time_ns; /* last set virtual time */
+
+static const void *time_handle;
+
+typedef struct {
+ uint64_t total_insn;
+ uint64_t quantum_insn; /* insn in last quantum */
+ int64_t last_quantum_time; /* time when last quantum started */
+} 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) max_insn_per_second;
+}
+
+static int64_t time_for_insn(uint64_t num_insn)
+{
+ double num_secs = (double) num_insn / (double) max_insn_per_second;
+ return num_secs * (double) NSEC_IN_ONE_SEC;
+}
+
+static void update_system_time(vCPUTime *vcpu)
+{
+ int64_t elapsed_ns = now_ns() - vcpu->last_quantum_time;
+ uint64_t max_insn = num_insn_during(elapsed_ns);
+
+ if (vcpu->quantum_insn >= max_insn) {
+ /* this vcpu ran faster than expected, so it has to sleep */
+ uint64_t insn_advance = vcpu->quantum_insn - max_insn;
+ uint64_t time_advance_ns = time_for_insn(insn_advance);
+ int64_t sleep_us = time_advance_ns / 1000;
+ g_usleep(sleep_us);
+ }
+
+ vcpu->total_insn += vcpu->quantum_insn;
+ vcpu->quantum_insn = 0;
+ vcpu->last_quantum_time = now_ns();
+
+ /* based on total number of instructions, what should be the new time? */
+ int64_t new_virtual_time = time_for_insn(vcpu->total_insn);
+
+ 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 vcpu_init(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+ vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+ vcpu->total_insn = 0;
+ vcpu->quantum_insn = 0;
+ vcpu->last_quantum_time = now_ns();
+}
+
+static void vcpu_exit(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+ vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+ update_system_time(vcpu);
+}
+
+static void every_quantum_insn(unsigned int cpu_index, void *udata)
+{
+ vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+ g_assert(vcpu->quantum_insn >= max_insn_per_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 quantum_insn =
+ qemu_plugin_scoreboard_u64_in_struct(vcpus, vCPUTime, quantum_insn);
+ /* count (and eventually trap) once per tb */
+ qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu(
+ tb, QEMU_PLUGIN_INLINE_ADD_U64, quantum_insn, n_insns);
+ qemu_plugin_register_vcpu_tb_exec_cond_cb(
+ tb, every_quantum_insn,
+ QEMU_PLUGIN_CB_NO_REGS, QEMU_PLUGIN_COND_GE,
+ quantum_insn, max_insn_per_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) {
+ max_insn_per_second = g_ascii_strtoull(tokens[1], NULL, 10);
+ if (!max_insn_per_second && errno) {
+ fprintf(stderr, "%s: couldn't parse %s (%s)\n",
+ __func__, tokens[1], g_strerror(errno));
+ return -1;
+ }
+ } else {
+ fprintf(stderr, "option parsing failed: %s\n", opt);
+ return -1;
+ }
+ }
+
+ vcpus = qemu_plugin_scoreboard_new(sizeof(vCPUTime));
+ max_insn_per_quantum = max_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_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 0b64d2c1e3..449ead1130 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
--
2.39.2
