why did Ubuntu turn off kernel preemption in Edgy?

Sivan Greenberg sivan at ubuntu.com
Tue Nov 28 09:15:42 GMT 2006


Rocco Stanzione wrote:
> Thus spake Adam Dingle:
>> In the Edgy kernel we've turned off CONFIG_PREEMPT, turning on
>> CONFIG_PREEMPT_VOLUNTARY instead (see the changelog excerpt below). This
>> change may not be great for multimedia users (especially those
>> editing audio) since it can increase latency. Out of curiosity, what was
>> the motivation for this?
> 
> I asked the same thing on #ubuntu-kernel on freenode.  After first being told 
> that the kernel *was* preemptible, I eventually confirmed that we are only 
> preempting the Big Kernel Lock, which isn't the same thing, and it was 
> explained that it was decided that since kernel preemption may not be 
> appropriate for everyone, it was disabled.  I suffer significantly from the 
> change, as my desktop gets mighty laggy during heavy i/o, of which there is 
> more than I would expect when I install packages.
> 

I'm also suffering the same lag while "heavy" i/o (e.g. , as Rocco noted 
, one package install) basically my whole system and UI gets terribly 
jerky. I'm suffering form this so much that I would even be willing to 
trade battery life for better performance. Can we please have the choice 
between the two modes? This is something not suitable for the average 
user to to tweak, but it would be nicer if we could switch between modes 
without having to rebuild a custom kernel ourselves.

Cheers,

Sivan



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