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Standard deviatation of interactivity (std_intvty) in result json is incorrectly calculated #300

@asb

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@asb

process_result.py calculates interactivity metrics from the time per output token (tpot) metrics:

for key, value in bmk_result.items():
    if key.endswith('ms'):
        data[key.replace('_ms', '')] = float(value) / 1000.0
    if 'tpot' in key:
        data[key.replace('_ms', '').replace('tpot', 'intvty')] = 1000.0 / float(value)

This is incorrect for the standard deviation - when the standard deviation is low, we'll produce a huge standard deviation of interactivity. Here's an example from a recent run:

  {
    "hw": "gb200",
    "tp": 36,
    "ep": 1,
    "dp_attention": "false",
    "conc": 512,
    "model": "/mnt/lustre01/models/deepseek-r1-0528-fp4-v2",
    "framework": "dynamo-trtllm",
    "precision": "fp4",
    "isl": 1024,
    "osl": 1024,
    "tput_per_gpu": 2423.747715243624,
    "output_tput_per_gpu": 1363.5939611144877,
    "input_tput_per_gpu": 10904.977748276717,
    "disagg": true,
    "num_prefill_gpu": 4,
    "num_decode_gpu": 32,
    "mtp": "on",
    "mean_ttft": 1.2919637345420085,
    "median_ttft": 0.4378697440261021,
    "std_ttft": 2.1574805073166776,
    "p99_ttft": 9.712858405703447,
    "mean_tpot": 0.009590339660491956,
    "mean_intvty": 104.27159364538116,
    "median_tpot": 0.009667698638864516,
    "median_intvty": 103.43723334320352,
    "std_tpot": 0.0009682636562182605,
    "std_intvty": 1032.7765516942895,
    "p99_tpot": 0.011633036075231341,
    "p99_intvty": 85.96208191335067,
    "mean_itl": 0.4402040011098412,
    "median_itl": 0.4408050079946406,
    "std_itl": 0.0884514747228438,
    "p99_itl": 0.8289496807963588,
    "mean_e2el": 10.116033398757338,
    "median_e2el": 9.590883667988237,
    "std_e2el": 2.3359472701507817,
    "p99_e2el": 18.67461088597775
  },

Unless you're able to get the figure from the benchmark harness, the simplest fix is probably to avoid calculating and emitting that field altogether.

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