how to convert txt to json?

i try use jq convert was successful, but I didn't get the results I wanted. I tried to get the results I wanted, but it's hard.

jq -Rs '[ split("\n")[] | select(length > 0) | split(" ") |  {group:.[0], instnace: .[1], value: .[2]} ]' input.txt

original txt file.. There are IP addresses and values ​​from cpu20 to 46 in total

cpu20 10.0.20.1 12
cpu20 10.0.20.1 22
cpu20 10.0.20.1 13
cpu20 10.0.20.1 11
cpu20 10.0.20.1 14

....~cpu46

It's the result of the way I tried. output json

{
    "group": "cpu-46",
    "instnace": "10.0.46.94",
    "value": "10"
  },
  {
    "group": "cpu-46",
    "instnace": "10.0.46.95",
    "value": "10"
  },
  {
    "group": "cpu-46",
    "instnace": "10.0.46.96",
    "value": "11"
  },
  {
    "group": "cpu-46",
    "instnace": "10.0.46.97",
    "value": "8"
  },
  {
    "group": "cpu-46",
    "instnace": "10.0.46.98",
    "value": "11"
  },
  {
    "group": "cpu-46",
    "instnace": "10.0.46.99",
    "value": "11"
  },
  {
    "group": "cpu-46",
    "instnace": "10.0.46.100",
    "value": "8"
  }

What should I do to get the results as follows?

    {
  "CPU20": [
    { "instance": "10.0.20.1", "value": 12 },
    { "instance": "10.0.20.2", "value": 22 },
    { "instance": "10.0.20.3", "value": 13 },
    { "instance": "10.0.20.4", "value": 11 },
    { "instance": "10.0.20.5", "value": 14 }
  ],
  "CPU21": [
    { "instance": "10.0.21.1", "value": 15 },
    { "instance": "10.0.21.2", "value": 24 },
    { "instance": "10.0.21.3", "value": 21 },
    { "instance": "10.0.21.4", "value": 15 },
    { "instance": "10.0.21.5", "value": 16 }
  ],
  "CPU22": [
    { "instance": "10.0.22.1", "value": 12 },
    { "instance": "10.0.22.2", "value": 18 },
    { "instance": "10.0.22.3", "value": 19 },
    { "instance": "10.0.22.4", "value": 12 },
    { "instance": "10.0.22.5", "value": 13 }
  ],
  "CPU23": [
    { "instance": "10.0.20.1", "value": 17 },
    { "instance": "10.0.20.2", "value": 15 },
    { "instance": "10.0.20.3", "value": 21 },
    { "instance": "10.0.20.4", "value": 22 },
    { "instance": "10.0.20.5", "value": 25 }
  ]
}

Using group_by and map

jq -Rn '
  [inputs | select(. != "") / " "]
  | group_by(.[0])
  | map({(.[0][0]): map({instance: .[1], value: .[2]})})
  | add
'

Demo

Using reduce

jq -Rn '
  reduce (inputs | select(. != "") / " ") as [$cpu, $instance, $value] ({};
    .[$cpu] += [{$instance, $value}]
  )
'

Demo
_{Improved by @JeffMercado}