Simpoints

Steps to profile, generate, and use SimPoints with gem5:

1. To profile workload and generate SimPoint BBV file, use the following option:

build/ARM/gem5.opt <base options> configs/example/fs.py --simpoint-profile [--simpoint-interval <interval length>] <rest of fs.py options>

This will generate a SimPoint Basic Block Vector file (named simpoint.bb.gz) in the gem5 run folder. SimPoint profiling should be run with a single AtomicSimpleCPU configuration and fastmem. Multicore simulation is not supported. <interval length> is in number of instructions. Default interval length is 10M instructions.

2. Generate SimPoint analysis using SimPoint 3.2 from UCSD. See http://cseweb.ucsd.edu/~calder/simpoint/index.htm for details. (SimPoint 3.2 not included in gem5 repository.)

A sample command to generate the SimPoint analysis based on the BBV file is as follows:

simpoint -loadFVFile simpoint.bb.gz -maxK 30 -saveSimpoints <simpoint_file> -saveSimpointWeights <weight_file> -inputVectorsGzipped

The gem5 flow currently does not support variable-length intervals.

3. To take gem5 checkpoints based on SimPoint analysis, use the following option:

build/ARM/gem5.opt <base options> configs/example/fs.py --take-simpoint-checkpoint=<simpoint file path>,<weight file path>,<interval length>,<warmup length> <rest of fs.py options>

<simpoint file> and <weight file> is generated by SimPoint analysis tool in Step #2 above. <interval length> and <warmup length> are in number of instructions. gem5 checkpoints will be generated <warmup length> instructions before the designated SimPoint starting points.

4. To resume from gem5 SimPoint checkpoints, use the following option:

build/ARM/gem5.opt <base options> configs/example/fs.py --restore-simpoint-checkpoint -r <N> --checkpoint-dir <simpoint checkpoint path> <rest of fs.py options>

<N> is (SimPoint index + 1). E.g., "-r 1" will resume from SimPoint #0.

This command will resume from a single specified SimPoint checkpoint. It will recognize the warmup period. After simulating the warmup period, gem5 statistics will be dumped and reset. After simulating the actual SimPoint, gem5 will automatically terminate. The simulations for all other SimPoints should be run separately. To project the full execution, the gem5 statistics from individual SimPoints must be weighted accordingly.

For questions or feedback on this flow, please contact Dam Sunwoo (dam.sunwoo@arm.com)