Performance: Reading JCIFS file in Android is slow

First of all, I saw an existing question ( JCIFS: Finding files is too slow to be used ), but that was for Java, not Android, and none of the suggested answers.

I created an Android project for Android SDK 25 (7.1.1) in Android Studio 2.3, linked the library with compile 'jcifs:jcifs:1.3.17'

and typed in the following simple test code. The result is below the code.

protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    jcifs.Config.setProperty("jcifs.util.loglevel", "3");
    //jcifs.Config.setProperty("jcifs.smb.client.dfs.disabled", "false");
    //jcifs.Config.setProperty("jcifs.resolveOrder", "DNS");

    try
    {
        NtlmPasswordAuthentication auth = new NtlmPasswordAuthentication("", ID, PASSWORD);
        final SmbFile smb = new SmbFile("smb://192.168.XX.XX/Share/FileName", auth);

        Thread t = new Thread(new Runnable()
        {
            @Override
            public void run()
            {
                Log.d(TAG, "Test Start");

                for(int i = 1000; i<10000; i+=1000)
                    measure(i);

                Log.d(TAG, "Test End");
            }

            private void measure(int bufferSize)
            {
                Log.d(TAG, "=====Buffer: " + bufferSize + "============");
                try
                {
                    byte[] buffer = new byte[bufferSize];
                    int read = 0;
                    InputStream str = smb.getInputStream();
                    long start = System.nanoTime();

                    while(read < 1000000)
                        read += str.read(buffer);

                    long end = System.nanoTime();
                    str.close();
                    float time = (float) ((end - start) / 1000000000d);
                    float speed = (float) read / 1048576 / time;
                    Log.d(TAG, "Time:" + time + ", size =" + read);
                    Log.d(TAG, "Speed =  " + speed + "MB/s");
                }
                catch(IOException exc)
                {
                    exc.printStackTrace();
                }
            }
        });
        t.start();
    }
    catch(Exception exc)
    {
        Log.d(TAG, exc.toString());
    }
}

      

        
        
        
      

    

Result

Test Start
=====Buffer: 1000============
Time:2.210785, size =1000000
Speed =  0.43137363MB/s
=====Buffer: 2000============
Time:1.4158936, size =1000000
Speed =  0.6735495MB/s
=====Buffer: 3000============
Time:1.0556641, size =1002000
Speed =  0.9051948MB/s
=====Buffer: 4000============
Time:0.7543335, size =1000000
Speed =  1.2642609MB/s
=====Buffer: 5000============
Time:3.6557617, size =1000000
Speed =  0.26086885MB/s
=====Buffer: 6000============
Time:3.292389, size =1002000
Speed =  0.2902396MB/s
=====Buffer: 7000============
Time:2.9179688, size =1001000
Speed =  0.32715496MB/s
=====Buffer: 8000============
Time:2.462616, size =1000000
Speed =  0.38726068MB/s
=====Buffer: 9000============
Time:3.9379272, size =1008000
Speed =  0.24411413MB/s
Test End

      

        
        
        
      

    

The read speed is about 0.2MB / s ~ 1.2MB / s. The device is connected to Wi-Fi 150 Mbps, so in theory it can reach above 10 Mbps. The SMB server isn't slow either. When I copied the file to my laptop, the read speed was around 30MB / s.

Why is it so slow? What should I check? Why is the read speed about 5 times faster (1.2 MB / s) when the buffer size is 4000?

BTW, I've tested copying the same file with other commercial applications. File Commander, Asus File Manager showed similarly low speeds, ES File Explorer showed about 2 MB / s, and Solid Explorer showed about 5 MB / s. Since I'm pretty sure they all use JCIFS (although maybe slightly different versions), there should be a way to achieve at least 5MB / s like Solid Explorer does.