Pierrick Bouvier <pierrick.bouv...@linaro.org> writes:
(Added Philip to CC)
> On 5/28/24 12:57, Alex Bennée wrote:
>> Pierrick Bouvier <pierrick.bouv...@linaro.org> writes:
>>
>>> On 5/28/24 12:14, Alex Bennée wrote:
>>>> 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.
<snip>
>>>>> +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.
>>>>
>>>
>>> More exactly, the assert we hit means that the idle callback, was not
>>> called before the resume callback.
>>> Any chance you can check what is the current vcpu->state value? I
>>> wonder if it's not an exited cpu, that gets resumed after.
>> No when I looked at it it was set as UNKNOWN. Unfortunately it
>> doesn't
>> trigger if I stick breakpoints in or run under rr.
>>
>
> By using rr record --chaos mode maybe?
Ahh yes that triggered it.
It looks like we have a race:
(rr) c
Continuing.
Thread 1 hit Hardware watchpoint 7: *(int *) 0x5559ba6899b0
Old value = -1
New value = 10
machvirt_init (machine=0x5559b9ac3c00) at ../../hw/arm/virt.c:2214
2214 numa_cpu_pre_plug(&possible_cpus->cpus[cs->cpu_index],
DEVICE(cpuobj),
(rr) c
Continuing.
[New Thread 650125.650142]
[Switching to Thread 650125.650142]
Thread 44 hit Breakpoint 8, mttcg_cpu_thread_fn (arg=0x5559ba6896e0) at
../../accel/tcg/tcg-accel-ops-mttcg.c:70
70 assert(tcg_enabled());
(rr) p cpu->cpu_index
$24 = 10
(rr) c
Continuing.
[Switching to Thread 650125.650125]
Thread 1 hit Breakpoint 10, cpu_common_realizefn (dev=0x5559ba6896e0,
errp=0x7fff02322c10) at ../../hw/core/cpu-common.c:205
205 Object *machine = qdev_get_machine();
(rr) p cpu->cpu_index
$25 = 10
(rr) bt
#0 cpu_common_realizefn (dev=0x5559ba6896e0, errp=0x7fff02322c10) at
../../hw/core/cpu-common.c:205
#1 0x00005559b606e6a5 in arm_cpu_realizefn (dev=0x5559ba6896e0,
errp=0x7fff02322c10) at ../../target/arm/cpu.c:2552
#2 0x00005559b63dd5d0 in device_set_realized (obj=0x5559ba6896e0,
value=true, errp=0x7fff02322d20) at ../../hw/core/qdev.c:510
#3 0x00005559b63e84e7 in property_set_bool (obj=0x5559ba6896e0,
v=0x5559ba681540, name=0x5559b68fafe1 "realized", opaque=0x5559b97f73c0,
errp=0x7fff02322d20)
at ../../qom/object.c:2354
#4 0x00005559b63e6065 in object_property_set (obj=0x5559ba6896e0,
name=0x5559b68fafe1 "realized", v=0x5559ba681540, errp=0x7fff02322d20) at
../../qom/object.c:1463
#5 0x00005559b63ead1d in object_property_set_qobject (obj=0x5559ba6896e0,
name=0x5559b68fafe1 "realized", value=0x5559ba681420, errp=0x5559b7810320
<error_fatal>)
at ../../qom/qom-qobject.c:28
#6 0x00005559b63e640a in object_property_set_bool (obj=0x5559ba6896e0,
name=0x5559b68fafe1 "realized", value=true, errp=0x5559b7810320 <error_fatal>)
at ../../qom/object.c:1533
#7 0x00005559b63dccbd in qdev_realize (dev=0x5559ba6896e0, bus=0x0,
errp=0x5559b7810320 <error_fatal>) at ../../hw/core/qdev.c:291
#8 0x00005559b5fe4243 in machvirt_init (machine=0x5559b9ac3c00) at
../../hw/arm/virt.c:2295
#9 0x00005559b5ada5d6 in machine_run_board_init (machine=0x5559b9ac3c00,
mem_path=0x0, errp=0x7fff02322f30) at ../../hw/core/machine.c:1576
#10 0x00005559b5eb416f in qemu_init_board () at ../../system/vl.c:2621
#11 0x00005559b5eb4482 in qmp_x_exit_preconfig (errp=0x5559b7810320
<error_fatal>) at ../../system/vl.c:2713
#12 0x00005559b5eb7088 in qemu_init (argc=35, argv=0x7fff02323268) at
../../system/vl.c:3759
#13 0x00005559b63d7ff2 in main (argc=35, argv=0x7fff02323268) at
../../system/main.c:47
Because looking at the order things happen in the specific CPU realisation:
qemu_init_vcpu(cs);
cpu_reset(cs);
acc->parent_realize(dev, errp);
And the common realize function doesn't get to do:
/* Plugin initialization must wait until the cpu start executing code */
#ifdef CONFIG_PLUGIN
if (tcg_enabled()) {
cpu->plugin_state = qemu_plugin_create_vcpu_state();
async_run_on_cpu(cpu, qemu_plugin_vcpu_init__async, RUN_ON_CPU_NULL);
}
#endif
before we've started executing.....
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
