golang复制文件花费太多时间

Question

I use the following code to copy files which works OK The problem is that when we use this method to copy folder and items like node_js project with node_modules inside in windows this can take a long time about 40 sec and in mac it takes 2 sec. when doing trace (print the copied files) we saw that for example the io.copy took 5 sec to copy short readme file or json file , in each run it get stuck on different files , small size files like json readme etch this is not consistent, in different run it stuck on different files ( if you run on same project).

we checked it on 3 different windows10 machine ( 1-3 years old) and 2 different macbook (3 years old) on exact same project. What it can be ?

func walk(src string, baseDir string, archive *zip.Writer) error {
   return filepath.Walk(src, func(path string, info os.FileInfo, err error) (e error) {
      if err != nil {
         return err
      }

      if info.IsDir() {
         return
      }

      header, err := zip.FileInfoHeader(info)
      if err != nil {
         return err
      }
      if baseDir != "" {
         header.Name = filepath.ToSlash(getRelativePath(path, baseDir))
      }

      header.Method = zip.Deflate
      writer, err := archive.CreateHeader(header)
      if err != nil {
         return err
      }

      file, err := os.Open(path)
      if err != nil {
         return err
      }
      defer func() {
         e = CloseFile(file, e)
      }()

      _, err = io.Copy(writer, file)
      return err
   })
}

we are checking it almost 4 days and we didnt find any pattern :(