print last 50 runs when using ai_pep_format (#28128)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28128
as title
Test Plan:
```
# ----------------------------------------
# PyTorch/Caffe2 Operator Micro-benchmarks
# ----------------------------------------
# Tag : short
# Benchmarking PyTorch: add
PyTorchObserver {"type": "add_M64_N64_K64_cpu", "metric": "latency", "unit": "ms", "value": "29.169559478759766"}
PyTorchObserver {"type": "add_M64_N64_K64_cpu", "metric": "latency", "unit": "ms", "value": "29.206514358520508"}
PyTorchObserver {"type": "add_M64_N64_K64_cpu", "metric": "latency", "unit": "ms", "value": "29.4950008392334"}
PyTorchObserver {"type": "add_M64_N64_K64_cpu", "metric": "latency", "unit": "ms", "value": "29.172897338867188"}
PyTorchObserver {"type": "add_M64_N64_K64_cpu", "metric": "latency", "unit": "ms", "value": "29.27255630493164"}
PyTorchObserver {"type": "add_M64_N64_K64_cpu", "metric": "latency", "unit": "ms", "value": "29.549837112426758"}
PyTorchObserver {"type": "add_M64_N64_K64_cpu", "metric": "latency", "unit": "ms", "value": "29.63113784790039"}
...
Reviewed By: hl475
Differential Revision: D17957611
fbshipit-source-id: 4e70ba2070b97fbbca0d6d4295abbead2ac356d4
