[Linux-ia64] [case closed] Re: web page on O(1) scheduler

From: Mike Galbraith <efault_at_gmx.de>
Date: 2003-05-28 01:16:28
At 06:25 PM 5/22/2003 +0200, Mike Galbraith wrote:
>At 11:52 AM 5/22/2003 +0200, Mike Galbraith wrote:
>>At 10:56 AM 5/21/2003 -0700, David Mosberger wrote:
>>> >>>>> On Wed, 21 May 2003 11:26:31 +0200, Mike Galbraith 
>>> <efault@gmx.de> said:
>>>   Mike> The page mentions persistent starvation.  My own explorations
>>>   Mike> of this issue indicate that the primary source is always
>>>   Mike> selecting the highest priority queue.
>>>My working assumption is that the problem is a bug with the dynamic
>>>prioritization.  The task receiving the signals calls sleep() after
>>>handling a signal and hence it's dynamic priority should end up higher
>>>than the priority of the task sending signals (since the sender never
>>>relinquishes the CPU voluntarily).
>>>However, I haven't actually had time to look at the relevant code, so
>>>I may be missing something.  If you understand the issue better,
>>>please explain to me why this isn't a dynamic priority issue.
>>You're right, it looks like a corner case.
>Out of curiosity, is someone hitting that with a real program?
>         -Mike
>if so, I suppose nano-ticks may be needed....

Since I spent a bunch of time fumbling around with this problem, I may as 
well post one last time and put it to bed.  I bet Ingo has a _lot_ better 
way to cure that problem, but...

Yes indeed, pedantic tracking of cpu usage does fix the problem.  It also 
makes for some interesting changes in contest numbers (well, _I_ find them 
interesting;)  If anyone wants to see the numbers, they're attached.  If 
anyone wants to try the attached diff, it's attached too, have fun... the 
standard "you get to keep the pieces" lkml warrantee applies :)  FWIW, it 
works just fine here, and the only time someone now manages to steal ticks 
(one) is (apparently) once in a long while when someone (whose initials 
appear to be IDE:) keeps interrupts disabled for too long.  Nobody has yet 
managed to steal more than one tick.

         The End,


P.S.  ok, so they're micro-ticks... what's a few orders of magnitude :) 

Received on Tue May 27 08:12:31 2003

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