Messages in this thread | | | Date | Wed, 11 May 2011 19:35:56 +0200 | From | Stephan Bärwolf <> | Subject | Re: [PATCH] sched: fix/optimise calculation of weight-inverse |
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>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
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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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