[gem5-users] Re: How to suspend FS simulation after certain number of ticks

[Jason Lowe-Power via gem5-users]

Hello,

Unfortunately, we don't have enough time to answer all questions in depth.
You may be able to find more help on either the gem5 slack
 or the gem5 youtube channel
. If you have access to ChatGPT Plus, you
can also use the gem5 GPT .
In fact, we have found that most of the LLMs do a good job answering
gem5-related questions.

In the meantime, here is the output from the gem5 GPT for your question.
This answer has not been checked for correctness, but our experience is
that the answers from the gem5 GPT at a minimum point in the right
direction.

Suspending and resuming a Full System (FS) simulation in gem5, similar to
what you've described for System-call Emulation (SE) mode, is indeed
possible. In FS mode, you can control the simulation flow using the Python
configuration scripts, just as you do in SE mode. However, there are some
nuances to consider when dealing with FS simulations.

For your specific use case, where you want to suspend the simulation after
a certain number of ticks, retrieve the `stats.txt` file, and then resume,
you can follow these steps:

1. **Modify the Python Script**:
   - Open the `/gem5/configs/example/riscv/fs_linux.py` script.
   - In this script, you can insert a loop that calls `m5.simulate()` for a
specified number of ticks. After each `m5.simulate()` call, the script will
regain control, allowing you to perform operations like dumping statistics.
   - Here's an example of how you might modify the script:

 ```python
 import m5
 from m5.objects import *

 # existing configuration code...

 num_ticks = 1e9  # Example: 1 billion ticks
 while m5.curTick() < num_ticks:
 m5.simulate(100)  # simulate for 1 million ticks at a time
 print("Current tick:", m5.curTick())
 m5.stats.dump()  # dump the stats
 ```

   - This script will now run the simulation in chunks of 1 million ticks,
dumping the statistics after each chunk.

2. **Dumping Statistics**:
   - The `m5.stats.dump()` call will update the `stats.txt` file. Make sure
you have set up your statistics correctly in the simulation configuration
so that they are captured and written to the file.

3. **Resuming the Simulation**:
   - The loop will automatically continue the simulation until it reaches
the specified number of ticks. There's no need for explicit "resume"
commands, as `m5.simulate()` both starts and resumes the simulation.

4. **Periodic Checkpoints (Optional)**:
   - If you want to be able to resume the simulation from a particular
point, not just dump statistics, consider using checkpoints. You can create
a checkpoint at each loop iteration or at

specific intervals. Here's how you can add checkpoint creation:

   ```python
   checkpoint_interval = 1e7  # Example: every 10 million ticks
   next_checkpoint = checkpoint_interval

   while m5.curTick() < num_ticks:
   m5.simulate(min(checkpoint_interval, num_ticks - m5.curTick()))
   print("Current tick:", m5.curTick())
   m5.stats.dump()  # dump the stats

   if m5.curTick() >= next_checkpoint:
   m5.checkpoint('checkpoint%d' % (m5.curTick()))
   next_checkpoint += checkpoint_interval
   ```

   - This will create a checkpoint file every 10 million ticks (or at the
specified interval).

5. **Considerations for FS Mode**:
   - In FS mode, especially with complex simulations, be aware that there
might be additional complications, such as device states and interactions
with the simulated OS. Always test your modified script to ensure that it
behaves as expected.

6. **Running the Modified Script**:
   - Once you've modified your `fs_linux.py` script, run it as you normally
would to start the simulation.

By following these steps, you should be able to achieve your goal of
suspending the FS simulation at specific tick intervals, dumping the stats,
and then resuming the simulation. Remember that gem5 is a complex tool, and
small changes in the simulation script can have significant impacts on the
behavior and performance of your simulation, so careful testing and
validation of your modified script are recommended.

On Tue, Jan 16, 2024 at 1:16 AM elio.vinciguerra--- via gem5-users <
gem5-users@gem5.org> wrote:

> Or, at least, I would need to do it in such a way as to have the
> historical progression of the "stats.txt" file during the simulation. So I
> need to suspend the simulation at a certain tick, get the "stats.txt" file,
> resume the simulation, or I need a solution that allows me to dump at a
> certain tick.
> ___
> gem5-users mailing list -- gem5-users@gem5.org
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>
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[gem5-users] Re: How to suspend FS simulation after certain number of ticks

[elio.vinciguerra--- via gem5-users]

Or, at least, I would need to do it in such a way as to have the historical 
progression of the "stats.txt" file during the simulation. So I need to suspend 
the simulation at a certain tick, get the "stats.txt" file, resume the 
simulation, or I need a solution that allows me to dump at a certain tick.
___
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