orchestration/simulators.py: speed up simulations using gem5 checkpoints

Currently, when a checkpoint is created in gem5 using the KVM CPU, the
simulated tick when the checkpoint is taken will end up in the few
seconds or more when the KVM CPU is slow. When the checkpoint is
afterwards restored, gem5 will continue the simulation at this tick.
This means that other, synchronized simulators first have to catch up,
essentially just synchronizing without performing any useful work.
Depending on their speed, this can take a lot of time and is especially
costly with a RTL simulator in the loop. To avoid this we now, by
default, edit the to be restored gem5 checkpoint to start at tick 0
instead.

experiments/simbricks/orchestration/experiment/experiment_environment.py

@@ -40,6 +40,9 @@ class ExpEnv(object):
         self.workdir = os.path.abspath(workdir)
         self.cpdir = os.path.abspath(cpdir)
         self.shm_base = self.workdir
+        self.utilsdir = f'{self.repodir}/experiments/simbricks/utils'
+        """Directory containing some utility scripts/binaries."""
+
         self.qemu_img_path = f'{self.repodir}/sims/external/qemu/build/qemu-img'
         self.qemu_path = (
             f'{self.repodir}/sims/external/qemu/build/'

experiments/simbricks/orchestration/simulators.py

@@ -431,6 +431,14 @@ class Gem5Host(HostSim):
         self.extra_main_args = []
         self.extra_config_args = []
         self.variant = 'fast'
+        self.modify_checkpoint_tick = True
+        """Whether to modify the event queue tick before restoring a checkpoint.
+        When this is enabled, the restored checkpoint will start at event queue
+        tick 0. This is a performance optimization since now, connected
+        simulators don't have to simulate and synchronize until the restored
+        tick before the actual workload can be executed. Disable this if you
+        need to retain the differences in virtual time between multiple gem5
+        instances."""
 
     def resreq_cores(self) -> int:
         return 1
@@ -439,7 +447,13 @@ class Gem5Host(HostSim):
         return 4096
 
     def prep_cmds(self, env: ExpEnv) -> tp.List[str]:
-        return [f'mkdir -p {env.gem5_cpdir(self)}']
+        cmds = [f'mkdir -p {env.gem5_cpdir(self)}']
+        if env.restore_cp and self.modify_checkpoint_tick:
+            cmds.append(
+                f'python3 {env.utilsdir}/modify_gem5_cp_tick.py --tick 0 '
+                f'--cpdir {env.gem5_cpdir(self)}'
+            )
+        return cmds
 
     def run_cmd(self, env: ExpEnv) -> str:
         cpu_type = self.cpu_type

experiments/simbricks/utils/__init__.py

+# Copyright 2023 Max Planck Institute for Software Systems, and
+# National University of Singapore
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

experiments/simbricks/utils/modify_gem5_cp_tick.py

+# Copyright 2023 Max Planck Institute for Software Systems, and
+# National University of Singapore
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+"""Script to modify the tick of a gem5 checkpoint."""
+
+import argparse
+import os
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        '--cpdir', help='Path to gem5 checkpoint directory', required=True
+    )
+    parser.add_argument(
+        '--tick',
+        help='The new value for the checkpoint\'s tick',
+        type=int,
+        required=True
+    )
+
+    args = parser.parse_args()
+
+    # Modify tick of all checkpoints in gem5 checkpoint directory to new_tick
+    for cp in filter(
+        lambda file: file.startswith('cpt.'), os.listdir(args.cpdir)
+    ):
+        cp_file = f'{args.cpdir}/{cp}/m5.cpt'
+        if not os.path.exists(cp_file):
+            print(
+                f'WARN {os.path.basename(__file__)}: checkpoint '
+                f'{args.cpdir}/{cp} doesn\'t have a m5.cpt'
+            )
+            continue
+        with open(cp_file, 'r', encoding='utf-8') as f:
+            data: str = f.read()
+        curtick = int(cp.split('.')[1])
+        newdata = data.replace(f'curTick={curtick}', f'curTick={args.tick}', 1)
+        with open(cp_file, 'w', encoding='utf-8') as f:
+            f.write(newdata)
+        print(
+            f'INFO {os.path.basename(__file__)}: successfully set tick of '
+            f'{args.cpdir}/{cp} to {args.tick}'
+        )
+
+
+if __name__ == '__main__':
+    main()