why did Ubuntu turn off kernel preemption in Edgy?

Flavio Martins xhaker at gmail.com
Wed Nov 29 17:50:11 GMT 2006

Can't argue with someone who can write like this. Knowledgeable.
Mental note: google before communicating with mjg59 ;)

(I guess this subject (preemption) was discussed for too long already)

BenC bring it on!

Flavio Martins

On 11/29/06, Matthew Garrett <mjg59 at srcf.ucam.org> wrote:
> On Wed, Nov 29, 2006 at 12:27:25PM -0500, Phillip Susi wrote:
> > 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.
> If the human eye is unable to distinguish movement at faster than the
> equivalent of 24 frames per second, then you'd see exactly the same
> thing in real life. You don't, which indicates that faster movement is
> still perceivable. In computer games, the difference between 30 frames
> per second and 60 frames per second is quite easy to distinguish.
> In reality, there is no concept of "frames per second" in the human
> visual system. The eye receptors are sufficiently sensitive that a
> single photon will produce a visible response[1]. The fact that we
> perceive 16 frames per second as smooth motion is an artifact of
> higher-level processing, not an indication that we're unable to perceive
> flicker above 16Hz - there's no well defined lower bound on the minimum
> period of time a stimulus has to appear for before it reaches higher
> levels of consciousness, and it varies between individuals. Even with
> continuous flickering (a worst case scenario for determining whether
> a stimulous is continuous or not), some people are able to perceive
> 120Hz flicker.
> > 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?
> If that were the case, you'd see the frames moving vertically. You
> don't. There's a shutter between the light and the film, as described in
> http://en.wikipedia.org/wiki/Movie_projector . On modern projectors, the
> shutter opens more than once per frame.
> [1] Sadly the spontaneous firing rate is higher than this, so a single
> photon is somewhere below the noise threshold
> --
> Matthew Garrett | mjg59 at srcf.ucam.org
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