tree b29fe7bdb55f2a25b6d42d288003a7eb37ec7ff6
parent aead8fb0fd1cb063a424bf68fb86577ff06681ea
author Jason Lowe-Power <jason@lowepower.com> 1662753711 -0700
committer Bobby Bruce <bbruce@ucdavis.edu> 1667419549 +0000

python,stdlib: Add multiprocessing module

This changeset replicates some of the multiprocessing module
implementation from the python standard library in gem5. The goal of
this and following changesets is to enable users to use a *single* set
of python scripts to run and analyze a suite of gem5 simulations.

We must reimplement some of the multiprocessing module becaue it is not
flexible enough to allow for customized command line parameter to the
"python" executable (gem5 in our case). To get around this, I extended
the Process and context objects to be gem5 specific.

The next steps is to wrap the Process and Pool types with gem5-specific
versions that will improve their usability for our needs. With this
changeset, these objects are usable, but it will require significant
user effort to reach the goal of running/analyzing many different gem5
simulations.

There are some limitation:
- The pool will only work if the max tasks per child is 1
- The functions that are executed must come from another module

As an example, the following code should work after applying this
change.

test.py:
```python
from gem5.utils.multiprocessing import Process, Pool
from sim import info, run_sim
if __name__ == '__m5_main__' or __name__ == '__main__':
    info('main line')
    p1 = Process(target=run_sim, args=('bob',))
    p2 = Process(target=run_sim, args=('jane',))
    p1.start()
    p2.start()
    p2.join()
    p1.join()
    with Pool(processes=4, maxtasksperchild=1) as pool:
        pool.map(run_sim, range(10))
```

sim.py:
```
import os
def info(title):
    print(title)
    print('module name:', __name__)
    print('parent process:', os.getppid())
    print('process id:', os.getpid())
def run_sim(name):
    info('function g')
    from gem5.prebuilt.demo.x86_demo_board import X86DemoBoard
    from gem5.resources.resource import Resource
    from gem5.simulate.simulator import Simulator
    board = X86DemoBoard()
    board.set_kernel_disk_workload(
        kernel=Resource("x86-linux-kernel-5.4.49"),
        disk_image=Resource("x86-ubuntu-18.04-img"),
    )
    simulator = Simulator(board=board)
    simulator.run(max_ticks=10000000)
```

Change-Id: I4348ebaa75d006949ec96e732f5dc2a5173c6048
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63432
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>