How do you calculate your retry budget? about finagle HOT 1 OPEN

import com.twitter.conversions.DurationOps._
import com.twitter.finagle.Backoff
import com.twitter.finagle.Http
import com.twitter.finagle.ServiceFactory
import com.twitter.finagle.http
import com.twitter.finagle.service.ReqRep
import com.twitter.finagle.service.ResponseClass
import com.twitter.finagle.service.ResponseClassifier
import com.twitter.finagle.service.RetryBudget
import com.twitter.util.Duration
import com.twitter.util.Future
import com.twitter.util.Return
import com.twitter.util.StorageUnit
import com.twitter.util.Timer

val host = "test.com"
val url = "https://test.com/test1"
val totalRequestTimeout = 5.seconds
val referenceTimeout =
    Duration.fromMilliseconds(
      Math.max(1L, totalRequestTimeout.inMillis / 5L - 100L)
    )
initialRequestTimeout =
    Duration.fromMilliseconds(referenceTimeout.inMillis * 2L)
val retryRequestTimeout =
    Duration.fromMilliseconds(referenceTimeout.inMillis * 3L)
val maxResponseSizeInBytes = 10000000
val clientFactory = Http.client
      .withRequestTimeout(initialRequestTimeout)
      .withRetryBudget(RetryBudget())
      .withRetryBackoff(Backoff.exponentialJittered(1.second, backoff))
      .withResponseClassifier(
        customResponseClassifierOnErrors orElse http.service.HttpResponseClassifier.ServerErrorsAsFailures
      )
      .withMaxResponseSize(
          StorageUnit.fromBytes(maxResponseSizeInBytes)
        )
      .withTls(host)
val client = clientFactory.newClient("test.com:443")
val requestBuilder = http
      .RequestBuilder()
      .url(url)
      .addHeader(
        http.Fields.UserAgent,
        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:50.0) Gecko/20100101 Firefox/50.0"
      ).addHeader(http.Fields.Host, host)

val request = requestBuilder.buildGet()
val response = httpClient.toResponse(request)
response