scriptencoding utf-8

function! s:benchmark() abort "{{{
  normal !gg
  call timer_start(0, function('s:callback', [reltime(), line('$')]), {'repeat': -1})
endfunction "}}}

function! s:callback(time, lines, timer) abort "{{{
  if line('.') < a:lines
    execute 'normal!' "\<C-f>"
    return
  endif
  echomsg reltimestr(reltime(a:time))
  call timer_stop(a:timer)
endfunction "}}}

command! -nargs=0 ScrollBench  call s:benchmark()