diff --git a/spec/measure_time_with_linux_source_code.lua b/spec/measure_time_with_linux_source_code.lua
new file mode 100644
index 0000000..adb82b9
--- /dev/null
+++ b/spec/measure_time_with_linux_source_code.lua
@@ -0,0 +1,143 @@
+local nio = require("nio")
+local Path = require("pathlib")
+local git = require("pathlib.git")
+local d = require("pathlib.utils.debug")
+
+local log = Path("measure.log"):absolute()
+log:io_write("")
+local fd = log:fs_open("a")
+assert(fd, log:tostring())
+function d.p(...) ---@diagnostic disable-line
+  vim.loop.fs_write(fd, d.ps(...) .. "\n")
+end
+
+---@alias after_func_cb fun(array: PathlibPath[])
+
+---@param dir PathlibPath
+---@param array PathlibPath[]
+---@param cb after_func_cb?
+local function scan_sync_rec(dir, array, cb)
+  for path in dir:iterdir() do
+    if path:is_dir() then
+      scan_sync_rec(path, array)
+    end
+    array[#array + 1] = path
+  end
+  if cb then
+    cb(array)
+  end
+end
+
+---@param dir PathlibPath
+---@param array PathlibPath[]
+---@param cb after_func_cb?
+local function scan_sync_depth(dir, array, cb)
+  for path in dir:iterdir({ depth = 100 }) do
+    array[#array + 1] = path
+  end
+  if cb then
+    cb(array)
+  end
+end
+
+---@param dir PathlibPath
+---@param array PathlibPath[]
+---@param cb after_func_cb?
+local function scan_async_iterdir(dir, array, cb)
+  local function _iterdir_cb(path, fs_type)
+    if fs_type == "directory" then
+      scan_async_iterdir(path, array, cb)
+    end
+    array[#array + 1] = path
+  end
+  dir:iterdir_async(_iterdir_cb, nil, function(_)
+    if cb then
+      cb(array)
+    end
+  end)
+end
+
+---@param dir PathlibPath
+---@param array PathlibPath[]
+---@param cb after_func_cb?
+local function scan_async_nuv(dir, array, cb)
+  local nuv = dir.nuv
+  local function _iterdir(path)
+    local h = nuv.fs_scandir(path:tostring())
+    if not h then
+      return
+    end
+    while true do
+      local name, fs_type = vim.loop.fs_scandir_next(h)
+      if not name or not fs_type then
+        break
+      end
+      if fs_type == "directory" then
+        _iterdir(path:child(name))
+      end
+      array[#array + 1] = path:child(name)
+    end
+  end
+  _iterdir(dir)
+  if cb then
+    cb(array)
+  end
+end
+
+---comment
+---@param name string
+---@param dir PathlibPath
+---@param func fun(dir: PathlibPath, array: PathlibPath[], cb: after_func_cb?)
+local function time_it(name, dir, func, times)
+  d.pf("==== Start %s (%s times) ====", name, times)
+  times = times or 1
+  local start = os.clock()
+  local counter = 0
+  local function run_func()
+    func(dir, {}, function(array)
+      counter = counter + 1
+      if counter < times then
+        run_func()
+      else
+        local elapsed = os.clock() - start
+        d.p(d.f("%s: (%.3f sec, %.3f ave) [# %06s]", name, elapsed, elapsed / times, #array))
+      end
+    end)
+  end
+  run_func()
+end
+
+d.p(vim.loop.os_homedir())
+local linux = Path("~/Documents/linux"):absolute()
+d.pf([[linux: %s]], linux)
+
+local url = [[https://github.com/torvalds/linux]]
+assert(linux:is_dir(true), string.format([[Please download %s into %s]], url, linux))
+
+local obj = vim.system({ "tree", "-a", "-f", linux:tostring() }):wait()
+local _, num_lines = obj.stdout:gsub("\n", "\t")
+d.pf([[TREE: %s]], num_lines - 3) -- files detected with `tree` command (uncount summary lines)
+
+local test_times = 5
+-- local test_times = 1
+
+nio.run(function()
+  time_it("scan_sync_rec", linux, scan_sync_rec, test_times)
+  time_it("scan_sync_depth", linux, scan_sync_depth, test_times)
+  -- time_it("scan_async_iterdir", linux, scan_async_iterdir, test_times)
+  time_it("scan_async_nuv", linux, scan_async_nuv, test_times)
+end)
+
+---@type PathlibPath[]
+local array = {}
+scan_async_nuv(linux, array)
+d.pf("scan_async_nuv done. %s files.", #array)
+git.fill_git_state_in_root(array, linux)
+local dot_git = linux:child(".git")
+for _, path in ipairs(array) do
+  if not path.git_state.ignored and not vim.startswith(path:tostring(), dot_git:tostring()) then
+    d.pp(path, d.g(path.git_state))
+  end
+end
+
+vim.loop.fs_close(fd)