Re: CFS review

On Thu, Aug 02, 2007 at 12:43:29PM +0200, Andi Kleen wrote:
However, I undertand why Ingo chose to use 64 bits. It has the advantage
that the numbers never wrap within 584 years. I'm well aware that it's
very difficult to keep tasks ordered according to a key which can wrap.

If you define an appropiate window and use some macros for the comparisons
it shouldn't be a big problem.

It should not, but the hardest thing is often to keep values sorted within a
window. When you store your values in a tree according to a key, it's not
always easy to do find the first one relative to a sliding offset.

But if we consider that we don't need to be more precise than the return
value from gettimeofday() that all applications use,

gettimeofday() has too strict requirements, that make it unnecessarily slow
for this task.

maybe we would use (TSC >> (x bits)) when TSC is available, or jiffies in other
cases. I believe that people not interested in high time accuracies are not
much interested in perfect fairness either. However, we should do the best to
avoid any form of starvation, otherwise we jump back to the problem with the
current scheduler.

every hour. We may accept to recompute all keys every hour.

You don't need to recompute keys; just use careful comparisons using
subtractions and a window. TCPs have done that for decades.

Have all keys use 32-bit resolution, and monitor the 32nd bit. All tasks

If you're worried about wrapping in one hour why is wrapping in two
hours not a problem?

I've not said I was worried about that (or maybe I explained myself poorly).
Even if it was once a minute, it would not bother me. I wanted to explain
that if the solution requires to do it that often, it should be acceptable.

I have one request though. If anybody adds anything complicated
for this please make it optional so that 64bit platforms are not
burdened by it.

Fair enough. But the solution is not there yet. Maybe once it's there, it
will be better than current design for all platforms and the only difference
will be the accuracy due to optional use of the TSC.

-Andi

Willy

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages

  • Re: Extending Ruler in Word
    ... Michel Bintener wrote: ... > normal view is still not enough for you, you can set the text to wrap ... > window, so you can see even more of your text. ... >> I have recently acquired a Mac G4. ...
    (microsoft.public.mac.office.word)
  • Re: OT:Global Warming Scandal!
    ... Do you hit return when nearing the right side of your input window? ... I've never seen the automatic line wrap undo an explicit ... I think the news servers no longer care about line length. ...
    (alt.autos.toyota)
  • Re: Getting a referenvce to a form
    ... what it *sounds* like to me is the TSC seeing a size change of its main ... wrap the window handle of the TSC. ... kiosk application to another application as a result of a UI event in the ... bool processSwitch; ...
    (microsoft.public.dotnet.framework.compactframework)
  • Re: Doublespacing
    ... Don't tell it to wrap to window. ... That's why I told you not to wrap it. ... If you tell it to wrap, it inserts a carriage return at the end of the ... carriage return which is going to fragment the display of the document ...
    (comp.sys.mac.system)
  • Re: Carriage return
    ... OE will appear to wrap to your ... composition window width as you type. ... The real wrapping based on your settings only occurs when the message is ...
    (microsoft.public.windows.inetexplorer.ie6_outlookexpress)