rollup.json

{
    "aggregations": [
        {
            "fieldName": "metric_with_total_count_of_events",
            "name": "total",
            "type": "longSum"
        },
        {
            "name": "rolledup",
            "type": "count"
        }
    ],
    "dataSource": "your_datasource",
    "dimensions": [
    ],
    "granularity": "DAY",
    "having": null,
    "intervals": "2017-11-16:00:00+00:00/2017-11-17T00:00:00+00:00",
    "queryType": "groupBy",
    "postAggregations": [
        {
            "fields": [
                {
                    "fields": [
                        {
                            "fieldName": "rolledup",
                            "type": "fieldAccess"
                        },
                        {
                            "fieldName": "total",
                            "type": "fieldAccess"
                        }
                    ],
                    "fn": "/",
                    "type": "arithmetic"
                },
                {
                    "type": "constant",
                    "value": 100
                }
            ],
            "fn": "*",
            "name": "rollup_perc",
            "type": "arithmetic"
        }
    ]
}