Response hook in script slows down the benchmark

[charz]

Just curious if anyone noticed if we put response (https://github.com/wg/wrk/blob/master/scripts/setup.lua#L26-L28) hook in lua script, that slows down the benchmark.

With Script

$ ./wrk -c 4 -t 2 -d 60 --timeout 300 -s scripts/setup.lua https://test.io/1GB.data
thread 1 created
thread 2 created
Running 1m test @ https://test.io/1GB.data
  2 threads and 4 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     0.00us    0.00us   0.00us    -nan%
    Req/Sec     0.00      0.00     0.00      -nan%
  0 requests in 1.00m, 0.98GB read
Requests/sec:      0.00
Transfer/sec:     16.72MB
thread 1 made 3 requests and got 0 responses
thread 2 made 2 requests and got 0 responses

Script without response function()

$ git diff scripts/setup.lua
diff --git a/scripts/setup.lua b/scripts/setup.lua
index 30d72f3..e3b2689 100644
--- a/scripts/setup.lua
+++ b/scripts/setup.lua
@@ -23,9 +23,9 @@ function request()
    return wrk.request()
 end

-function response(status, headers, body)
-   responses = responses + 1
-end
+--function response(status, headers, body)
+--   responses = responses + 1
+--end

 function done(summary, latency, requests)
    for index, thread in ipairs(threads) do
    
$ ./wrk -c 4 -t 2 -d 60 --timeout 300 -s scripts/setup.lua https://test.io/1GB.data
thread 1 created
thread 2 created
Running 1m test @ https://test.io/1GB.data
  2 threads and 4 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     3.14s   824.71ms   6.39s    81.08%
    Req/Sec     1.69      3.42    10.00     86.89%
  74 requests in 1.00m, 76.44GB read
Requests/sec:      1.23
Transfer/sec:      1.27GB
thread 1 made 43 requests and got 0 responses
thread 2 made 36 requests and got 0 responses

Without script

$ ./wrk -c 4 -t 2 -d 60 --timeout 300  https://test.io/1GB.data
Running 1m test @ https://test.io/1GB.data
  2 threads and 4 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     3.39s     1.26s    6.52s    79.10%
    Req/Sec     0.80      2.22    10.00     93.94%
  67 requests in 1.00m, 68.88GB read
  Non-2xx or 3xx responses: 1
Requests/sec:      1.12
Transfer/sec:      1.15GB