The tp90 is a minimum time under which 90% of requests have been served.
tp90 = top percentile 90
Imagine you have response times:
10s 1000s 100s 2s
Calculating TP is very simple:
1. Sort all times in ascending order: [2s, 10s, 100s, 1000s]
2. find latest item in portion you need to calculate. 2.1 For TP50 it will be ceil(4*0.5) = 2 requests. You need 2nd request. 2.2 For TP90 it will be ceil(4*0.9) = 4. You need 4th request.
3. We get time for the item found above. TP50=10s. TP90=1000s