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SubjectRe: [PATCH] sched: fix/optimise calculation of weight-inverse
>I think what we wanted to do was minimize the error:
> err = weight - inv*WMULT_CONST

Hi all,
thanks for your fast response.
I think what you mean is:

err = | WMULT_CONST - inv*weight | --> min

right?

But the following table(s) shows the difference in the inverses:
(assuming WMULT_CONST = 2**32 as on x64)

weight oldway
inv_weigth new inv_weight

1 2147483649 (=1+2**31)
4294967295 [=(2**32)-1]
2
1431655766 2147483647
3 (= WEIGHT_IDLEPRIO) 1073741824 1431655765
15 (= nice 19)
268435456 286331153
1024 (=nice 0)
4190212 4194304
...
...
88761 (=nice -20)
48387 48388

----

weight err
oldway err newway

1 2147483647 (=2**31 - 1)
1
2 1431655764
2
3 (= WEIGHT_IDLEPRIO) 1073741824 1
15 (= nice 19) 268435456 1
1024 (=nice 0)
4190208 0
...
...
88761 (=nice -20) 88789
28



Thus the "err" of the old way can become very large (up to about 2^31 ).
And of course the new error increases with increasing weight, it is
still alway
smaller than the oldway err (because oldway inv converts to newway inv)...


regards Stephan

--
Dipl.-Inf. Stephan Bärwolf
Ilmenau University of Technology, Integrated Communication Systems Group
Phone: +49 (0)3677 69 2821, FAX: +49 (0)3677 69 1614
Email: stephan.baerwolf@tu-ilmenau.de,
Web: http://www.tu-ilmenau.de/iks


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