why did Ubuntu turn off kernel preemption in Edgy?

Phillip Susi psusi at cfl.rr.com
Wed Nov 29 17:27:25 GMT 2006

Matthew Garrett wrote:
> doesn't mean that humans are unable to see the difference. If you point 
> a film camera at a wheel and accelerate it, viewers will see the wheel 
> speed up, slow down and then reverse. The brain is able to process 
> information at a greater rate than 24 frames per second, and the missing 
> information is noticed under certain circumstances.

No, this is the beat again.  You are being shown images that show the 
wheel more than 180 degrees out of phase with the previous and next 
images, which is the same as if it were going backwards at a slower 
rate.  If the wheel is spinning at 23 rpm and the film is 24 fps, then 
you get a 1 Hz beat.

> The second issue is the refresh rate at which humans will perceive 
> flicker. This varies depending on the individual, but to remove flicker 
> requires a refresh rate of much more than 24Hz. Cinema projectors 
> typically illuminate each frame twice, giving a refresh rate of 48Hz. 
> More modern equipment may do it at 72Hz. Whether flicker is noticable 
> depends on a combination of factors, including screen brightness, size 
> and how tired the viewer is.

What are you talking about?  The light source in the projector is always 
on and 24 film frames pass in front of it each second.  Where is the 
double illumination?

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