Windows system timer granularity

While running one of my apps on a Windows 10 VM I noticed that the timing was much different to that seen on the host PC. After lots of digging I finally found that the granularity of the system timer on the VM was around 16ms versus around 0.5ms on the host PC. My app is using some 1-5 millisecond sleeps but when the granularity is 16ms then 1ms becomes 16! (The actual granularity is 15.6ms due to a default 64Hz timer frequency).

Some cool resources on the web related to this:

Solved my problems by setting the granularity to the minimum supported by the PC; this setting remains in place until the application exits. So it just seems that my VM doesn’t have anything running that would otherwise cause the timer to run more quickly than the default (of 64Hz), whereas my development PC must have all sorts that are running the timer flat out; probably one reason my battery goes down more quickly than expected!

To query and change the granularity I used theses methods via C#:

I then wrote a little wrapper class to let me play with the timings using the .Net TimeSpan. Note: this is a frustrating struct to use because it really doesn’t want to use fractions of a millisecond without more than a bit of persuasion, specifically because FromMilliseconds will only consider the requested value to the nearest millisecond.

/// <summary>
/// Utility to query the timer resolution
/// </summary>
class TimerResolution
{
    [DllImport("ntdll.dll", SetLastError = true)]
    private static extern int NtQueryTimerResolution(out int MinimumResolution, out int MaximumResolution, out int CurrentResolution);


    [DllImport("ntdll.dll", SetLastError = true)]
    private static extern int NtSetTimerResolution(int DesiredResolution, bool SetResolution, out int CurrentResolution);


    private static TimeSpan TimeSpanFrom100nsUnits(int valueIn100nsUnits)
    {
        var nanoseconds = (double)valueIn100nsUnits * 100.0;
        var seconds = nanoseconds / 1000000000.0;
        var ticks = seconds * System.Diagnostics.Stopwatch.Frequency;
        var timeSpan = TimeSpan.FromTicks((long)ticks);
        return timeSpan;
    }


    private static (TimeSpan min, TimeSpan max, TimeSpan cur) Query()
    {
        NtQueryTimerResolution(out var min, out var max, out var cur);
        return (min: TimeSpanFrom100nsUnits(min), max: TimeSpanFrom100nsUnits(max), cur: TimeSpanFrom100nsUnits(cur));
    }


    /// <summary>Gets the minimum timer resolution</summary>
    public static TimeSpan MinResolution => Query().min;


    /// <summary>Gets the maximum timer resolution</summary>
    public static TimeSpan MaxResolution => Query().max;


    /// <summary>Gets/sets the current timer resolution</summary>
    public static TimeSpan CurrentResolution
    {
        get { return Query().cur; }

        set
        {
            var valueInSeconds = value.TotalMilliseconds / 1000.0;
            var valueInNanoseconds = valueInSeconds * 1000000000.0;
            var valueIn100Nanoseconds = (int)(valueInNanoseconds / 100.0);
            NtSetTimerResolution(DesiredResolution: valueIn100Nanoseconds, SetResolution: true, out _);
        }
    }
}

A little test app on my VM produced these results…

Minimum resolution:   15.6ms
Maximum resolution:   0.5ms
Current resolution:   15.6ms

Attempt to change to 2ms
Current resolution:   00:00:00.0020000
DateTime granularity: 00:00:00.0020970
Sleep 0:              00:00:00.0000009
Sleep 1:              00:00:00.0020053

Attempt to change to 5ms
Current resolution:   00:00:00.0050000
DateTime granularity: 00:00:00.0050328
Sleep 0:              00:00:00.0000012
Sleep 1:              00:00:00.0049719

Attempt to change to 0.5ms
Current resolution:   00:00:00.0005000
DateTime granularity: 00:00:00.0005471
Sleep 0:              00:00:00.0000008
Sleep 1:              00:00:00.0011774

Attempt to change to 15.6ms
Current resolution:   00:00:00.0156250
DateTime granularity: 00:00:00.0156280
Sleep 0:              00:00:00.0000011
Sleep 1:              00:00:00.0155707

Raspberry Pi Desktop virtual machine

This weekend I discovered that there is a Linux distribution, Debian Jessie, that now has the Raspberry Pi Desktop, download from here.

So I installed it as a virtual machine on my Windows 10 PC using VMWare Professsional Pro 14. The only difficulty was getting VMWare Tools working to allow automatic screen resizing and file sharing. Found some good info on the VMWare communities site (search for vmware tools debian jessie). From this thread there is a great perl script to help install VMWare Tools. The only modification I made was to delete –default from the line that runs the VMWare installer, without which the script will suggest an alternative option and abandon the installation.

I made a YouTube video of my virtual machine installation and VMWare tools configuration:

 

The script for VMWare tools:

#!/bin/bash 
 
sudo apt-get update 
sudo apt-get upgrade 
echo "Do go and mount your cdrom from the VMware menu" 
echo "press any key to continue" 
read -n 1 -s 
mount /dev/cdrom 
cd /media/cdrom0 
cp VMwareTools-*.tar.gz /tmp 
cd /tmp 
tar xvzf VMwareTools-*.tar.gz 
cd vmware-tools-distrib/ 
sudo apt-get install --no-install-recommends libglib2.0-0 
sudo apt-get install --no-install-recommends build-essential 
sudo apt-get install --no-install-recommends gcc-4.3 linux-headers-`uname -r` 
sudo ./vmware-install.pl 
 
sudo /etc/init.d/networking stop 
sudo rmmod pcnet32 
sudo rmmod vmxnet 
sudo modprobe vmxnet 
sudo /etc/init.d/networking start

 

 

 

VMWare Windows 10 expand/partition problem

Intro

I had a Windows 10 VM, managed using VMWare Workstation Pro 12. The VM was originally created with the default 60GB hard disk.

I needed to expand the disk, so I shutdown the VM, removed all snapshots, expanded the virtual HD to 120GB, and rebooted the VM. The plan was to use Windows 10’s disk management tool to expand the original partition and merge in the new partition.

But the recovery partition was sandwiched between the original and new partitions, and couldn’t be deleted using the Disk Management tool:

Untitled picture.png

I found the basics of how to fix this on the VMWare knowledge base. I’m adding my procedure here because it includes some useful screenshots.

Steps

I ran diskpart to work with partitions. (I ran as admin, but don’t think it was required.)

1Untitled picture

From the DISKPART shell, I then used the following to select and then remove the unwanted partition:

DISKPART> list volume

Volume ### Ltr Label Fs Type Size Status Info
 ---------- --- ----------- ----- ---------- ------- --------- --------
* Volume 0 D DVD-ROM 0 B No Media
 Volume 1 C NTFS Partition 59 GB Healthy System
 Volume 2 NTFS Partition 450 MB Healthy Hidden

DISKPART> select volume 2

Volume 2 is the selected volume.

DISKPART> delete partition override

DiskPart successfully deleted the selected partition.

The Disk Management window showed the new partition layout:

2Untitled picture.png

Next, I right-clicked on the C: partition and chose ‘Extend Volume’:

4.png

567

At last, a single 120GB partition.

8

🙂