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SubjectRe: fair group scheduler not so fair?
On Wed, May 28, 2008 at 12:35:19PM -0600, Chris Friesen wrote:
> Srivatsa Vaddagiri wrote:
>
>> We seem to be skipping the last element in the task list always. In your
>> case, the lone task in Group a/b is always skipped because of this.
>
>> Updated patch (on top of 2.6.26-rc3 +
>> http://programming.kicks-ass.net/kernel-patches/sched-smp-group-fixes/)
>> below. Pls let me know how it fares!
>
> Looking much better, but still some fairness issues with more complex
> setups.
>
> pid 2477 in A, others in B
> 2477 99.5%
> 2478 49.9%
> 2479 49.9%
>
> move 2478 to A
> 2479 99.9%
> 2477 49.9%
> 2478 49.9%
>
> So far so good. I then created C, and moved 2478 to it. A 3-second "top"
> gave almost a 15% error from the desired behaviour for one group:
>
> 2479 76.2%
> 2477 72.2%
> 2478 51.0%
>
>
> A 10-sec average was better, but we still see errors of 6%:

So it is converging to a fair state. How does it look
across say 20 or 30 seconds your side?

> 2478 72.8%
> 2477 64.0%
> 2479 63.2%
>
>
> I then set up a scenario with 3 tasks in A, 2 in B, and 1 in C. A
> 10-second "top" gave errors of up to 6.5%:
> 2500 60.1%
> 2491 37.5%
> 2492 37.4%
> 2489 25.0%
> 2488 19.9%
> 2490 19.9%
>
> a re-test gave errors of up to 8.1%:
>
> 2534 74.8%
> 2533 30.1%
> 2532 30.0%
> 2529 25.0%
> 2530 20.0%
> 2531 20.0%
>
> Another retest gave perfect results initially:
>
> 2559 66.5%
> 2560 33.4%
> 2561 33.3%
> 2564 22.3%
> 2562 22.2%
> 2563 22.1%
>
> but moving 2564 from group A to C and then back to A disturbed the perfect
> division of time and resulted in almost the same utilization pattern as
> above:
>
> 2559 74.9%
> 2560 30.0%
> 2561 29.6%
> 2564 25.3%
> 2562 20.0%
> 2563 20.0%
>

This is over a longer duration or a 10 second duration?

--
regards,
Dhaval


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