In gaming, input lag is defined as the delay between the when a user does something with an input device and when that action is reflected on the monitor.

The definition is straightforward, but the reality of input lag is much more subtle than may readily be apparent. There are many smaller latencies that contribute to the overall whole of input lag and understanding the full situation may prove beneficial to gamers everywhere.

The first subtlety is that there will always be input lag. Input lag is an unavoidable reality that can only be minimized and never eliminated. It will always take some amount of time for input data to get to the software and it will always take some amount of time for the software to use that data to display a frame of animation on the monitor. Keeping this total time as low as possible is a key mission of hardcore twitch gamers out there.

This article will step through all the different contributors to input lag, and we'll give some general estimates on the impact of each different contributor. Exact numbers will vary widely with different hardware and software combinations. But knowing where to focus when optimizing for input latency should help those who are interested.

After drilling down into the causes of input latency, we will provide a few examples of different hardware and settings in our lab. The extra twist is that we will be evaluating actual input latency using a high speed camera to count frames between input activation and monitor response. We'll be looking at three different games with multiple settings on both CRT and LCD monitors.

Reflexes and Input Generation
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  • DerekWilson - Monday, July 20, 2009 - link

    This is how we disable vsync.

    We got the same results in lag with present interval set to either 1 or 0 ... it really didn't make a measurable difference in our testing.
    Reply
  • DerekWilson - Monday, July 20, 2009 - link

    to clarify a little, this is why i think that Gamebryo (or Bethesda) must do some sort of internal timing that strictly enforces framerate, CPU time, or something based on some other factor than present interval. Reply
  • NetSoerfer - Monday, July 20, 2009 - link

    On page 5, the fifth paragraph begins with "If our frametime is just longer than 16.67ms...". The next paragraph is meant to describe the opposite but begins with "When framerate is lower than refresh rate...".

    Longer frametime equals lower refresh rate. The second paragraph should read "When framerate is higher than refresh rate..." or "When frametime is shorter than refresh rate...".
    Reply
  • DerekWilson - Monday, July 20, 2009 - link

    No, the next paragraph is not meant to describe the opposite case ...

    The first paragraph you cite describes the effects of double-buffered vsync on framerates both lower than refresh (first half of the paragraph) and higher than refresh (second half of the paragraph).

    The second paragraph you cite describes the effects of a 1 frame flip-queue with vsync or triple buffering on framerates that are lower than refresh.

    Sorry if that wasn't clear.
    Reply
  • Per Hansson - Sunday, July 19, 2009 - link

    Hi, I tried your recommendation with "overclocking" the mouse (erm, we are really just changing the speed of the USB port, not the mouse right?)

    Anyway, I've got a MS IntelliMouse Explorer v3.0
    When I run "Direct Input Mouse Rate" it shows my lag as 8ms at 125hz...

    So I used the driver hidusbf and changed the frequency to 1000hz, this resulted in 1.4ms and 700hz with my mouse...

    But now to begin with I had the mouse speed set to max in the Intellipoint mouse setup, and also "enhance pointer precision" enabled...

    And at 125hz / 8ms lag that gave me a good speed, a bit slower than I had in Win2K but still acceptable (current os is XP x64)
    But now with my "overclocked" mouse the movement is waaay to slow, I need a bigger mousepad to move the mousepointer all across my monitor
    Is this intended or just due to MS drivers or whatever?

    I was planning on getting the Microsoft Habu gaming mouse developed by Razer because the current iteration of the Explorer 3.0 is a POS with crap microbuttons that keep failing, think I've been through 3 of these in the last 2 years, even replaced them with ones bought at Elfa but they also failed after a couple months
    Anyway, will all mouse have this speed issue at high ouse rates? (above 125hz)
    Reply
  • MarktheC - Monday, July 27, 2009 - link

    Re: "But now with my "overclocked" mouse the movement is waaay to slow, I need a bigger mousepad to move the mousepointer all across my monitor. Is this intended or just due to MS drivers or whatever?"

    Yes, this is "how it works" (but it can be fixed).

    What's happening is this: At 125 Hz and a given on-the-pad mouse speed, each mouse report might be returning (say) 16 counts/report.
    The XP/Vista/7 "Enhance pointer precision" code uses the "16" value to lookup an acceleration curve (SmoothMouseXCurve/SmoothMouseYCurve) and apply a scaling factor to the mouse input (approx x 1.4 when the mouse count is 16). The pointer moves ~1.4 * 16 = ~22 pixels.

    If the report rate is changed to to 1000 Hz, each mouse report returns 2, 2, 2, 2, 2, 2, 2, 2 instead (same gross movement of 16, but spread over 8 times as many reports). Now the XP/Vista/7 "Enhance pointer precision" code uses "2" to lookup the acceleration curve and returns a scaling factor (~0.6 when the mouse count is 2). The pointer moves ~0.6 * 2 * 8 = ~9 pixels and you perceive the mouse as slow.

    This is (somewhat) described here:
    http://www.codinghorror.com/blog/archives/000977.h...">http://www.codinghorror.com/blog/archives/000977.h...
    http://www.microsoft.com/whdc/archive/pointer-bal....">http://www.microsoft.com/whdc/archive/pointer-bal....

    BUT Microsoft made a silly design mistake!:
    http://donewmouseaccel.blogspot.com/2009/06/out-of...">http://donewmouseaccel.blogspot.com/200...t-of-syn...

    A solution is to tweak the Registry: HKEY_CURRENT_USER\Control Panel>Mouse>SmoothMouseXCurve and SmoothMouseYCurve values.
    Treat each group of 4 bytes as a 32-bit integer, and divide by 8 (for 1000 Hz). AFAIK, doing this for both SmoothMouseYCurve & SmoothMouseXCurve should return the acceleration back to normal.

    A BETTER solution may be to stick with "Enhance pointer precision" and 125 Hz for normal Windows work, and use 1000 Hz only for gaming AND TURN OFF "Enhance pointer precision" when gaming (if required by the game: most modern games uses DirectX to read the mouse, which ignores the "Enhance pointer precision" checkbox anyway).

    Re: "I was planning on getting the Microsoft Habu ... will all mouse have this speed issue at high mouse rates? (above 125hz)"

    I don't know: I expect the Habu driver will do the right thing and not need any fix as above, but I don't know...
    Reply
  • DerekWilson - Monday, July 20, 2009 - link

    Actually ... the report / second rate should have zero impact on the speed of the pointer. I do say should -- something odd could be happening like it could be dropping counts in order to assemble reports that fast (i.e. your mouse could be too overclocked and might be doing things wrong). But I am not a hardcore mouse overclocker myself so I'd do a little research on it.

    I would recommend, if your mouse can't actually hit 1000Hz, to drop it down to 500 reports/second instead of 1000 ... it should be more consistent that way, and maybe it will fix your pointer speed issue.

    The CPI (reported as DPI) will have an impact on pointer speed. But so will things like setting mouse speed to maximum and using "enhance pointer precision" ... though these latter two don't really have desirable results.

    I strongly recommend leaving mouse speed at the middle notch ... setting it higher actually skips pixels (though "enhance pointer precisions" makes your mouse able to move one pixel at a time if you move it really slowly). And I also recommend not using "enhance pointer precision" as well ...

    These MS pointer ballistics can cause problems in older games, but if the developer did the "right" thing and used either DirectInput or raw input devices then the pointer speed settings shouldn't affect games (only the sensitivity slider in the game should affect pointer speed if it's done right). In most cases going forward you should be able to use the OS to manipulate your pointer speed without negatively impacting your game ... but there is a chance that these settings could negatively impact your gaming experience if the developer used a less desirable way to access the mouse data.
    Reply
  • Per Hansson - Monday, July 20, 2009 - link

    Thanks, the behaviour is the same at 250hz and 500hz
    Those rates just slow down the mouse more...

    There would be no way at all that I could set the mouse speed slider to the middle and get used to that, same for not having enhance pointer precision on

    Guess sometimes you just can't win eh? ;)
    In fact I was quite annoyed by the change in ballistics going from Win2K which supported acceleration which I used and really liked to WinXP which only has this "enhance pointer precision" option
    Reply
  • Xcrypt - Thursday, November 20, 2014 - link

    You shouldn't enable enhance pointer precision, nor should you have your mouse speed set to maximum. Both will adversely affect your ability to aim, especially the acceleration will. Reply
  • valnar - Sunday, July 19, 2009 - link

    "It is possible to overclock your mouse."

    Now I've seen everything. :)
    Reply

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