Pierrick Bouvier <pierrick.bouv...@linaro.org> writes:
> This plugin uses the new time control interface to make decisions
> about the state of time during the emulation. The algorithm is
> currently very simple. The user specifies an ips rate which applies
> per core. If the core runs ahead of its allocated execution time the
> plugin sleeps for a bit to let real time catch up. Either way time is
> updated for the emulation as a function of total executed instructions
> with some adjustments for cores that idle.
>
> 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
>
> Signed-off-by: Pierrick Bouvier <pierrick.bouv...@linaro.org>
> ---
> contrib/plugins/ips.c | 239 +++++++++++++++++++++++++++++++++++++++
> contrib/plugins/Makefile | 1 +
> 2 files changed, 240 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 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);
I'm triggering a weird race here:
(gdb) b vcpu_init
Breakpoint 1 at 0x7ffff7fa15f7: file
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c, line 127.
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program:
/home/alex/lsrc/qemu.git/builds/arm.debug/qemu-system-aarch64 -machine
type=virt,virtualization=on,pflash0=rom,pflash1=efivars -cpu cortex-a57 -smp 32
-accel tcg -device virtio-net-pci,netdev=unet -device virtio-scsi-pci -device
scsi-hd,drive=hd -netdev user,id=unet,hostfwd=tcp::2222-:22 -blockdev
driver=raw,node-name=hd,file.driver=host_device,file.filename=/dev/zen-ssd2/trixie-arm64,discard=unmap
-serial mon:stdio -blockdev
node-name=rom,driver=file,filename=/home/alex/lsrc/qemu.git/builds/arm.debug/pc-bios/edk2-aarch64-code.fd,read-only=true
-blockdev
node-name=efivars,driver=file,filename=/home/alex/images/qemu-arm64-efivars -m
8192 -object memory-backend-memfd,id=mem,size=8G,share=on -kernel
/home/alex/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image -append
root=/dev/sda2\ console=ttyAMA0 -plugin contrib/plugins/libips.so,ips=1000000000
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffe72006c0 (LWP 360538)]
[New Thread 0x7fffe68006c0 (LWP 360540)]
[New Thread 0x7fffe5e006c0 (LWP 360541)]
[New Thread 0x7fffe54006c0 (LWP 360542)]
[New Thread 0x7fffe4a006c0 (LWP 360543)]
[New Thread 0x7fffdfe006c0 (LWP 360544)]
[New Thread 0x7fffdf4006c0 (LWP 360545)]
[New Thread 0x7fffdea006c0 (LWP 360546)]
[Switching to Thread 0x7fffdf4006c0 (LWP 360545)]
Thread 8 "qemu-system-aar" hit Breakpoint 1, vcpu_init
(id=10457908569352202058, cpu_index=0) at
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
(gdb) c
Continuing.
[New Thread 0x7fffde0006c0 (LWP 360548)]
[Switching to Thread 0x7fffdea006c0 (LWP 360546)]
Thread 9 "qemu-system-aar" hit Breakpoint 1, vcpu_init
(id=10457908569352202058, cpu_index=1) at
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
(gdb)
Continuing.
[New Thread 0x7fffdd6006c0 (LWP 360549)]
[Switching to Thread 0x7fffde0006c0 (LWP 360548)]
Thread 10 "qemu-system-aar" hit Breakpoint 1, vcpu_init
(id=10457908569352202058, cpu_index=2) at
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
(gdb)
Continuing.
[New Thread 0x7fffdcc006c0 (LWP 360550)]
[Switching to Thread 0x7fffdd6006c0 (LWP 360549)]
Thread 11 "qemu-system-aar" hit Breakpoint 1, vcpu_init
(id=10457908569352202058, cpu_index=3) at
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
(gdb)
Continuing.
[New Thread 0x7fffd3e006c0 (LWP 360551)]
[Switching to Thread 0x7fffdcc006c0 (LWP 360550)]
Thread 12 "qemu-system-aar" hit Breakpoint 1, vcpu_init
(id=10457908569352202058, cpu_index=4) at
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
(gdb) n
129 set_start_time();
(gdb)
131 vcpu->counter = num_insn_during(uptime_ns());
(gdb)
132 vcpu_set_state(vcpu, EXECUTING);
(gdb)
133 }
(gdb) p vcpu->state
$1 = EXECUTING
(gdb) p &vcpu->state
$2 = (vCPUState *) 0x555557c6b5d0
(gdb) watch *(vCPUState *) 0x555557c6b5d0
Hardware watchpoint 2: *(vCPUState *) 0x555557c6b5d0
(gdb) c
Continuing.
[Thread 0x7fffdfe006c0 (LWP 360544) exited]
[Thread 0x7fffe5e006c0 (LWP 360541) exited]
Thread 12 "qemu-system-aar" hit Hardware watchpoint 2: *(vCPUState *)
0x555557c6b5d0
Old value = EXECUTING
New value = IDLE
vcpu_set_state (vcpu=0x555557c6b5c0, new_state=IDLE) at
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:83
83 }
(gdb) c
Continuing.
[New Thread 0x7fffdfe006c0 (LWP 360591)]
[New Thread 0x7fffe5e006c0 (LWP 360592)]
[New Thread 0x7fffd34006c0 (LWP 360593)]
[Switching to Thread 0x7fffdfe006c0 (LWP 360591)]
Thread 14 "qemu-system-aar" hit Breakpoint 1, vcpu_init
(id=10457908569352202058, cpu_index=6) at
/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
(gdb)
Continuing.
[New Thread 0x7fffd2a006c0 (LWP 360594)]
**
ERROR:/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:144:vcpu_resume:
assertion failed: (vcpu->state == IDLE)
Bail out!
ERROR:/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:144:vcpu_resume: assertion
failed: (vcpu->state == IDLE)
Thread 13 "qemu-system-aar" received signal SIGABRT, Aborted.
[Switching to Thread 0x7fffd3e006c0 (LWP 360551)]
__pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6,
no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
44 ./nptl/pthread_kill.c: No such file or directory.
(gdb) bt
#0 __pthread_kill_implementation (threadid=<optimized out>,
signo=signo@entry=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
#1 0x00007ffff4ca9e8f in __pthread_kill_internal (signo=6,
threadid=<optimized out>) at ./nptl/pthread_kill.c:78
#2 0x00007ffff4c5afb2 in __GI_raise (sig=sig@entry=6) at
../sysdeps/posix/raise.c:26
#3 0x00007ffff4c45472 in __GI_abort () at ./stdlib/abort.c:79
#4 0x00007ffff6e46ec8 in () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#5 0x00007ffff6ea6e1a in g_assertion_message_expr () at
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#6 0x00007ffff7fa16e2 in vcpu_resume (id=10457908569352202058, cpu_index=5)
at /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:144
#7 0x00005555562c3202 in plugin_vcpu_cb__simple (cpu=0x5555583d9540,
ev=QEMU_PLUGIN_EV_VCPU_RESUME) at ../../plugins/core.c:111
#8 0x00005555562c43f7 in qemu_plugin_vcpu_resume_cb (cpu=0x5555583d9540) at
../../plugins/core.c:523
#9 0x0000555555d9150e in qemu_wait_io_event (cpu=0x5555583d9540) at
../../system/cpus.c:465
#10 0x00005555562c67d0 in mttcg_cpu_thread_fn (arg=0x5555583d9540) at
../../accel/tcg/tcg-accel-ops-mttcg.c:118
#11 0x00005555565120ff in qemu_thread_start (args=0x5555584716e0) at
../../util/qemu-thread-posix.c:541
#12 0x00007ffff4ca8134 in start_thread (arg=<optimized out>) at
./nptl/pthread_create.c:442
#13 0x00007ffff4d287dc in clone3 () at
../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
(gdb)
But I don't understand how we can ever hit the idle callback without
first hitting the init callback.
> + 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
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
