stdlib,configs,tests: Add gem5 MultiSim (MultiProcessing for gem5) (#1167)

This allows for multiple gem5 simulations to be spawned from a single
parent gem5 process, as defined in a simgle gem5 configuration. In this
design _all_ the `Simulator`s are defined in the simulation script and
then added to the mutlisim module. For example:

```py
from gem5.simulate.Simulator import Simulator
import gem5.utils.multisim as multisim

# Construct the board[0] and board[1] as you wish here...

simulator1 = Simulator(board=board[0], id="board-1")
simulator2 = Simulator(board=board[1], id="board-2")

multisim.add_simulator(simulator1)
multisim.add_simulator(simulator2)
```

This specifies that two simulations are to be run in parallel in
seperate threads: one specified by `simulator1` and another by
`simulator2`. They are then added to MultiSim via the
`multisim.add_simulator` function. The user can specify an id via the
Simulator constructor. This is used to give each process a unique id and
output directory name. Given this, the id should be a helpful name
describing the simulation being specified. If not specified one is
automatically given.

To run these simulators we use `<gem5 binary> -m gem5.utils.multisim
<script> -p <num_processes>`. Note: multisim is an executable module in
gem5. This is the same module we input into our scripts to add the
simulators. This is an intentionally modular encapsulated design. When
the module processes a script it will schedule multiple gem5 jobs and,
dependent on the number of processes specified, will create child gem5
processes to processes tjese jobs (jobs are just gem5 simulations in
this case). The `--processes` (`-p`) argument is optional and if not
specified the max number of processes which can be run concurrently will
be the number of available threads on the host system.

The id for each process is used to create a subdirectory inside the
`outputdor` (`m5out`) of that id name. E.g, in the example above the
ID's are `board-1` and `board-2`. Therefore the m5 out directory will
look as follows:

```sh
- m5out
    - board-1
        - stats.txt
        - config.ini
        - config.json
        - terminal.out
    - board-2
        - stats.txt
        - config.ini
        - config.json
        - terminal.out
```

Each simulations output is encapsulated inside the subdirectory of the
id name.

If the multisim configuation script is passed directly to gem5 (like a
traditional gem5 configuraiton script, i.e.: `<gem5 binary> <script>`),
the user may run a single simulation specified in that script by passing
its id as an argument. E.g. `<gem5 binary> <script> board-1` will run
the `board-1` simulation specified in `script`. If no argument is passed
an Exception is raised asking the user to either specify or use the
MultiSim module if multiprocessing is needed.

If the user desires a list of ids of the simulations specified in a
given MultiSim script, they can do so by passing the `--list` (`-l`)
parameter to the config script. I.e., `<gem5 binary> <script> --list`
will list all the IDs for all the simulations specified in`script`.

This change comes with two new example scripts found in
'configs/example/gem5_library/multsim" to demonstrate multisim in both
an SE and FS mode simulation. Tests have been added which run these
scripts as part of gem5' Daily suite of tests.

Notes
=====

* **Bug fixed**: The `NoCache` classic cache hierarchy has been modified
so the Xbar is no longet set with a `__func__` call. This interfered
with MultiProcessing as this structure is not serializable via Pickle.
This was quite bad design anyway so should be changed

* **Change**: `readfile_contents` parameter previously wrote its value
to a file called "readfile" in the output dorectory. This has been
changed to write to a file called "readfile_{hash}" with "{hash}" being
a hash of the `readfile_contents`. This ensures that, during multisim
running, this file is not overwritten by other processes.

* **Removal note**: This implementation supercedes the functionality
outlined in 'src/python/gem5/utils/multiprocessing'. As such, this code
has been removed.

Limitations/Things to Fix/Improve
=================================

* Though each Simulator process has its own output directory (a
subdirectory within m5out, with an ID set by the user unique to that
Simulator), the stdout and stderr are still output to the terminal, not
the output directory. This results in: 1. stdout and stderr data lost
and not recorded for these runs. 2. An incredibly noisy terminal output.
* Each process uses the same cached resources. While there are locks on
resources when downloading, each processes will hash the resources they
require to ensure they are valid. This is very inefficient in cases
where resources are common between processes (e.g., you may have 10
processes each using the same disk image with each processes hashing the
disk images independently to give the same result to validate the
resources).

Change-Id: Ief5a3b765070c622d1f0de53ebd545c85a3f0eee

---------

Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Co-authored-by: Jason Lowe-Power <jason@lowepower.com>

tests/gem5/arm_boot_tests/configs/arm_boot_exit_run.py

@@ -222,9 +222,9 @@ board.set_kernel_disk_workload(
 simulator = Simulator(board=board)
 
 if args.tick_exit:
-    simulator.run(max_ticks=args.tick_exit)
-else:
-    simulator.run()
+    simulator.set_max_ticks(args.tick_exit)
+
+simulator.run()
 
 print(
     "Exiting @ tick {} because {}.".format(

tests/gem5/checkpoint_tests/configs/arm-hello-save-checkpoint.py

@@ -70,9 +70,9 @@ board.set_se_binary_workload(
     )
 )
 
-sim = Simulator(board=board, full_system=False)
-max_ticks = 10**6
-sim.run(max_ticks=max_ticks)
+sim = Simulator(board=board, full_system=False, max_ticks=10**6)
+
+sim.run()
 print(
     "Exiting @ tick {} because {}.".format(
         sim.get_current_tick(), sim.get_last_exit_event_cause()

tests/gem5/checkpoint_tests/configs/power-hello-save-checkpoint.py

@@ -73,9 +73,9 @@ board.set_se_binary_workload(
     obtain_resource("power-hello", resource_version="1.0.0")
 )
 
-sim = Simulator(board=board, full_system=False)
-max_ticks = 10**6
-sim.run(max_ticks=max_ticks)
+sim = Simulator(board=board, full_system=False, max_ticks=10**6)
+
+sim.run()
 print(
     "Exiting @ tick {} because {}.".format(
         sim.get_current_tick(), sim.get_last_exit_event_cause()

tests/gem5/checkpoint_tests/configs/sparc-hello-save-checkpoint.py

@@ -76,9 +76,8 @@ board.set_se_binary_workload(
     )
 )
 
-sim = Simulator(board=board, full_system=False)
-max_ticks = 10**6
-sim.run(max_ticks=max_ticks)
+sim = Simulator(board=board, full_system=False, max_ticks=10**6)
+sim.run()
 print(
     "Exiting @ tick {} because {}.".format(
         sim.get_current_tick(), sim.get_last_exit_event_cause()

tests/gem5/checkpoint_tests/configs/x86-fs-restore-checkpoint.py

@@ -85,10 +85,10 @@ board.set_kernel_disk_workload(
     ),
 )
 
-sim = Simulator(board=board, full_system=True)
+sim = Simulator(board=board, full_system=True, max_ticks=10**10)
 print("Beginning simulation!")
 
-sim.run(max_ticks=10**10)
+sim.run()
 
 print(
     "Exiting @ tick {} because {}.".format(

tests/gem5/checkpoint_tests/configs/x86-fs-save-checkpoint.py

@@ -87,11 +87,11 @@ board.set_kernel_disk_workload(
     disk_image=obtain_resource("x86-ubuntu-18.04-img"),
 )
 
-sim = Simulator(board=board, full_system=True)
+sim = Simulator(board=board, full_system=True, max_ticks=10**6)
 print("Beginning simulation!")
 
-max_ticks = 10**6
-sim.run(max_ticks=max_ticks)
+
+sim.run()
 print(
     "Exiting @ tick {} because {}.".format(
         sim.get_current_tick(), sim.get_last_exit_event_cause()

tests/gem5/checkpoint_tests/configs/x86-hello-save-checkpoint.py

@@ -76,9 +76,9 @@ board.set_se_binary_workload(
     )
 )
 
-sim = Simulator(board=board, full_system=False)
-max_ticks = 10**6
-sim.run(max_ticks=max_ticks)
+sim = Simulator(board=board, full_system=False, max_ticks=10**6)
+
+sim.run()
 print(
     "Exiting @ tick {} because {}.".format(
         sim.get_current_tick(), sim.get_last_exit_event_cause()

tests/gem5/gem5_library_example_tests/ref/simout_multisim_print_this_list.txt

@@ -0,0 +1,5 @@
+process_0
+process_1
+process_2
+process_3
+process_4

tests/gem5/gem5_library_example_tests/test_gem5_library_examples.py

@@ -348,6 +348,86 @@ gem5_verify_config(
     length=constants.long_tag,
 )
 
+gem5_verify_config(
+    name="test-gem5-library-example-multisim-fs-x86-npb",
+    fixtures=(),
+    verifiers=(),
+    config=joinpath(
+        config.base_dir,
+        "configs",
+        "example",
+        "gem5_library",
+        "multisim",
+        "multisim-fs-x86-npb.py",
+    ),
+    config_args=[],
+    gem5_args=["-m", "gem5.utils.multisim"],
+    valid_isas=(constants.all_compiled_tag,),
+    valid_hosts=constants.supported_hosts,
+    length=constants.long_tag,
+)
+
+gem5_verify_config(
+    name="test-gem5-library-example-multisim-print-this",
+    fixtures=(),
+    verifiers=(),
+    config=joinpath(
+        config.base_dir,
+        "configs",
+        "example",
+        "gem5_library",
+        "multisim",
+        "multisim-print-this.py",
+    ),
+    config_args=[],
+    gem5_args=["-m", "gem5.utils.multisim"],
+    valid_isas=(constants.all_compiled_tag,),
+    valid_hosts=constants.supported_hosts,
+    length=constants.quick_tag,
+)
+
+gem5_verify_config(
+    name="test-gem5-library-example-multisim-print-this-list",
+    fixtures=(),
+    verifiers=(
+        verifier.MatchStdoutNoPerf(
+            joinpath(getcwd(), "ref/simout_multisim_print_this_list.txt")
+        ),
+    ),
+    config=joinpath(
+        config.base_dir,
+        "configs",
+        "example",
+        "gem5_library",
+        "multisim",
+        "multisim-print-this.py",
+    ),
+    config_args=["--list"],
+    gem5_args=[],
+    valid_isas=(constants.all_compiled_tag,),
+    valid_hosts=constants.supported_hosts,
+    length=constants.quick_tag,
+)
+
+gem5_verify_config(
+    name="test-gem5-library-example-multisim-print-this-single-process",
+    fixtures=(),
+    verifiers=(),
+    config=joinpath(
+        config.base_dir,
+        "configs",
+        "example",
+        "gem5_library",
+        "multisim",
+        "multisim-print-this.py",
+    ),
+    config_args=["process_1"],
+    gem5_args=[],
+    valid_isas=(constants.all_compiled_tag,),
+    valid_hosts=constants.supported_hosts,
+    length=constants.quick_tag,
+)
+
 # The LoopPoint-Checkpointing feature is still under development, therefore
 # these tests are temporarily disabled until this feature is complete.#
 

tests/gem5/riscv_boot_tests/configs/riscv_boot_exit_run.py

@@ -173,9 +173,9 @@ board.set_workload(workload)
 simulator = Simulator(board=board)
 
 if args.tick_exit:
-    simulator.run(max_ticks=args.tick_exit)
-else:
-    simulator.run()
+    simulator.set_max_ticks(args.tick_exit)
+
+simulator.run()
 
 print(
     "Exiting @ tick {} because {}.".format(

tests/gem5/suite_tests/configs/suite_run_workload.py

@@ -145,9 +145,9 @@ board.set_workload(list(suite)[0])
 simulator = Simulator(board=board, full_system=args.fs_sim)
 
 if args.tick_exit:
-    simulator.run(max_ticks=args.tick_exit)
-else:
-    simulator.run()
+    simulator.set_max_ticks(args.tick_exit)
+
+simulator.run()
 
 print(
     "Exiting @ tick {} because {}.".format(

tests/gem5/to_tick/configs/tick-to-max.py

@@ -112,9 +112,9 @@ if args.set_ticks_before:
 simulator = Simulator(board=motherboard)
 
 if args.set_ticks_at_execution:
-    simulator.run(max_ticks=args.set_ticks_at_execution)
-else:
-    simulator.run()
+    simulator.set_max_ticks(args.set_ticks_at_execution)
+
+simulator.run()
 
 # Set the max ticks after the simulator run.
 if args.set_ticks_after:

tests/gem5/x86_boot_tests/configs/x86_boot_exit_run.py

@@ -201,9 +201,9 @@ print("Beginning simulation!")
 simulator = Simulator(board=motherboard)
 
 if args.tick_exit:
-    simulator.run(max_ticks=args.tick_exit)
-else:
-    simulator.run()
+    simulator.set_max_tick(args.tick_exit)
+
+simulator.run()
 
 print(
     "Exiting @ tick {} because {}.".format(