why did Ubuntu turn off kernel preemption in Edgy?

Hervé Fache Herve at lucidia.net
Tue Nov 28 19:19:11 GMT 2006

Well, reaction time is different from drop out in music and different
from eye perception.

If a system 'reacts' to user input in less than 70ms, users will have
the sensation that there is no delay.

If there is a gap of 3ms in your music, you start detecting it.

How do I know? Worked on car radios for a while, and display reaction
time was important (more than 100ms makes you feel the system is slow,
probably because the brain has the time to do a context switch and
needs to switch back ;-), just like the gaps in music when the RDS
'tests' another frequency (sound off, tune to f2, check signal
quality, tune to f1, sound on: all that in less than 3ms).

I suppose eyes can detect flicker because of the big difference
between pixel on and pixel off: you do not see the screen on and off,
but you perceive that there is flicker.

Too long post already, I shall stop here.

On 11/28/06, Jan Claeys <lists at janc.be> wrote:
> Considering that a human brain can unconsciously detect the difference
> between 65 Hz (flickers for most people) & 75 Hz (doesn't flicker for
> most people) CRT screen refresh rate, why wouldn't it be able to
> (unconsciously) detect a 100 ms latency?  65 Hz means that pixels get
> lighter and darker a bit inside every 15 ms interval.  75 Hz means that
> pixels get lighter and darker a bit inside every 13 ms interval.
> Similarly, I think that maybe (most) people don't hear the latency
> difference *consciously*, but it might still be irritating them because
> what's played when they press a key is just a tiny little bit off the
> right beat that they intended it to be on.
> --
> Jan Claeys

More information about the ubuntu-devel mailing list