The fix in https://github.com/pytorch/pytorch/pull/155446 addressed the "stack empty" issue that's easily reproducible on CPython 3.12.0-4. While this issue can also appear in other versions, it's not as easy to reproduce there.
I recently found a new cause for this problem.
1df5d00145/Python/ceval.c (L5807-L5836)
In the CPython 3.10 implementation, PyTrace_C_CALL and PyTrace_C_RETURN/PyTrace_C_EXCEPTION are supposed to appear in pairs. However, when c_profilefunc is changed, unexpected PyTrace_C_RETURN/PyTrace_C_EXCEPTION events can occur.
Here is the code to reproduce this problem.
```
import threading
import time
import torch
from threading import Event, Lock
lock = Lock()
lock.acquire()
event1 = Event()
event2 = Event()
event3 = Event()
def run():
event1.set()
event2.wait()
lock.acquire()
event3.set()
threading.Thread(target=run).start()
with torch.profiler.profile(activities=[torch.profiler.ProfilerActivity.CPU], with_stack=True):
event1.wait()
event2.set()
time.sleep(1)
with torch.profiler.profile(activities=[torch.profiler.ProfilerActivity.CPU], with_stack=True):
lock.release()
event3.wait()
```
<img width="1766" height="1250" alt="image" src="https://github.com/user-attachments/assets/6794eeca-7364-429e-91eb-62cdad116bd3" />
To fix this problem, we can record active_frames_ and remaining_start_frames_ for each thread, and when the PyTrace_C-RETURN/PyTrace_CEXT CEPTION event occurs, we can determine whether to record this event based on these two fields.
In reality, even without this fix, the final data appears to be right since the match process can handle this case (it would just result in an exception log being printed).
Do you think the fix is necessary?
Pull Request resolved: https://github.com/pytorch/pytorch/pull/159574
Approved by: https://github.com/sraikund16
Hi team,
Please help review this patch.
This PR https://github.com/pytorch/pytorch/pull/150370 tried to fix the "Empty C Call Queue" problem on Python 3.12. It added C calls for each starting Python event with a callable.
I found the root cause is not that we cannot get C function frames by `PyFrame_GetBack` when PythonTracer is filling start frames, but the c call event loss problem bug on Python 3.12.0-3.12.4. And that problem was fixed by 257c413cd1 on 3.12.5.
So I think the https://github.com/pytorch/pytorch/pull/150370 cannot fix the problem, this patch reverts the change of it.
There are solutions to fix the problem correctly, such as we can add a new monitoring callback to compensate call events of methods with C function or we can override the callback registered by `PyEval_SetProfile`. These solutions may make the code hard to maintain.
~~Since upgrading the micro version of Python is not difficult for users, we can just ignore C functions and suggest user upgrade.~~
Pull Request resolved: https://github.com/pytorch/pytorch/pull/155446
Approved by: https://github.com/sraikund16
Hi team,
Please help review this patch.
This PR https://github.com/pytorch/pytorch/pull/150370 tried to fix the "Empty C Call Queue" problem on Python 3.12. It added C calls for each starting Python event with a callable.
I found the root cause is not that we cannot get C function frames by `PyFrame_GetBack` when PythonTracer is filling start frames, but the c call event loss problem bug on Python 3.12.0-3.12.4. And that problem was fixed by 257c413cd1 on 3.12.5.
So I think the https://github.com/pytorch/pytorch/pull/150370 cannot fix the problem, this patch reverts the change of it.
There are solutions to fix the problem correctly, such as we can add a new monitoring callback to compensate call events of methods with C function or we can override the callback registered by `PyEval_SetProfile`. These solutions may make the code hard to maintain.
~~Since upgrading the micro version of Python is not difficult for users, we can just ignore C functions and suggest user upgrade.~~
Pull Request resolved: https://github.com/pytorch/pytorch/pull/155446
Approved by: https://github.com/sraikund16
Hi team,
Please help review this patch.
This PR https://github.com/pytorch/pytorch/pull/150370 tried to fix the "Empty C Call Queue" problem on Python 3.12. It added C calls for each starting Python event with a callable.
I found the root cause is not that we cannot get C function frames by `PyFrame_GetBack` when PythonTracer is filling start frames, but the c call event loss problem bug on Python 3.12.0-3.12.4. And that problem was fixed by 257c413cd1 on 3.12.5.
So I think the https://github.com/pytorch/pytorch/pull/150370 cannot fix the problem, this patch reverts the change of it.
There are solutions to fix the problem correctly, such as we can add a new monitoring callback to compensate call events of methods with C function or we can override the callback registered by `PyEval_SetProfile`. These solutions may make the code hard to maintain.
~~Since upgrading the micro version of Python is not difficult for users, we can just ignore C functions and suggest user upgrade.~~
Pull Request resolved: https://github.com/pytorch/pytorch/pull/155446
Approved by: https://github.com/sraikund16, https://github.com/cyyever
