Why are .NET timers limited to 15 ms resolution?

Question

Note that I\'m asking about something that will call a callback function more often than once every 15 ms using something like System.Threading.Timer. I\'m not

Answer 1

The timer resolution is given by the system heartbeat. This typically defaults to 64 beats/s which is 15.625 ms. However there are ways to modify these system wide settings to achieve timer resolutions down to 1 ms or even to 0.5 ms on newer platforms:

1. Going for 1 ms resolution by means of the multimedia timer interface:

The multimedia timer interface is able to provide down to 1 ms resolution. See About Multimedia Timers (MSDN), Obtaining and Setting Timer Resolution (MSDN), and this answer for more details about timeBeginPeriod. Note: Don't forget to call the timeEndPeriod to switch back to the default timer resolution when done.

How to do:

#define TARGET_RESOLUTION 1         // 1-millisecond target resolution

TIMECAPS tc;
UINT     wTimerRes;

if (timeGetDevCaps(&tc, sizeof(TIMECAPS)) != TIMERR_NOERROR) 
{
   // Error; application can't continue.
}

wTimerRes = min(max(tc.wPeriodMin, TARGET_RESOLUTION), tc.wPeriodMax);
timeBeginPeriod(wTimerRes); 

//       do your stuff here at approx. 1 ms timer resolution

timeEndPeriod(wTimerRes); 

Note: This procedure is availble to other processes as well and the obtained resolution applies system wide. The highest resoltion requested by any process will be active, mind the consequences.

2. Going to 0.5 ms resolution:

You may obtain 0.5 ms resolution by means of the hidden API NtSetTimerResolution(). NtSetTimerResolution is exported by the native Windows NT library NTDLL.DLL. See How to set timer resolution to 0.5ms ? on MSDN. Nevertheless, the true achievable resoltion is determined by the underlying hardware. Modern hardware does support 0.5 ms resolution. Even more details are found in Inside Windows NT High Resolution Timers. The supported resolutions can be obtained by a call to NtQueryTimerResolution().

How to do:

#define STATUS_SUCCESS 0
#define STATUS_TIMER_RESOLUTION_NOT_SET 0xC0000245

// after loading NtSetTimerResolution from ntdll.dll:

// The requested resolution in 100 ns units:
ULONG DesiredResolution = 5000;  
// Note: The supported resolutions can be obtained by a call to NtQueryTimerResolution()

ULONG CurrentResolution = 0;

// 1. Requesting a higher resolution
// Note: This call is similar to timeBeginPeriod.
// However, it to to specify the resolution in 100 ns units.
if (NtSetTimerResolution(DesiredResolution ,TRUE,&CurrentResolution) != STATUS_SUCCESS) {
    // The call has failed
}

printf("CurrentResolution [100 ns units]: %d\n",CurrentResolution);
// this will show 5000 on more modern platforms (0.5ms!)

//       do your stuff here at 0.5 ms timer resolution

// 2. Releasing the requested resolution
// Note: This call is similar to timeEndPeriod 
switch (NtSetTimerResolution(DesiredResolution ,FALSE,&CurrentResolution) {
    case STATUS_SUCCESS:
        printf("The current resolution has returned to %d [100 ns units]\n",CurrentResolution);
        break;
    case STATUS_TIMER_RESOLUTION_NOT_SET:
        printf("The requested resolution was not set\n");   
        // the resolution can only return to a previous value by means of FALSE 
        // when the current resolution was set by this application      
        break;
    default:
        // The call has failed

}

Note: The functionality of NtSetTImerResolution is basically mapped to the functions timeBeginPeriod and timeEndPeriod by using the bool value Set (see Inside Windows NT High Resolution Timers for more details about the scheme and all its implications). However, the multimedia suite limits the granularity to milliseconds and NtSetTimerResolution allows to set sub-millisecond values.

Answer 2

Perhaps the document linked here explains it a bit. It's kinda dry so I only browsed it quickly :)

Quoting the intro:

The system timer resolution determines how frequently Windows performs two main actions:

• Update the timer tick count if a full tick has elapsed.
• Check whether a scheduled timer object has expired.

A timer tick is a notion of elapsed time that Windows uses to track the time of day and thread quantum times. By default, the clock interrupt and timer tick are the same, but Windows or an application can change the clock interrupt period.

The default timer resolution on Windows 7 is 15.6 milliseconds (ms). Some applications reduce this to 1 ms, which reduces the battery run time on mobile systems by as much as 25 percent.

Originally from: Timers, Timer Resolution, and Development of Efficient Code (docx).

Answer 3

All replays here are about system timer resolution. But .net timers not respect it. As author notice by himself:

that the runtime implements its own timer queue that is similar to the Timer Queue Timers, but never actually calls the Win32 functions.

And Jan pointed in comment.

So, answers above are good info, but not directly correlated to .net timers and therefore misleading people :(

Short answer to both author questions is by design. Why did they decide to go this way? Feared about whole system performance? Who knows...
To not duplicate, see more info on both questions (and ways to implement precise timers on .net) in Jan's correlated topic.