From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri, 27 Jun 2008 11:41:32 +0000 (+0200)
Subject: sched: optimize effective_load()
X-Git-Tag: v2.6.27-rc1~1105^2~19
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cb5ef42a03a13f95a9ea94e6cda4f7a47497871f;p=pandora-kernel.git

sched: optimize effective_load()

s_i = S * rw_i / \Sum_j rw_j

 -> \Sum_j rw_j = S * rw_i / s_i

 -> s'_i = S * (rw_i + w) / (\Sum_j rw_j + w)

delta s = s' - s = S * (rw + w) / ((S * rw / s) + w)
        = s * (S * (rw + w) / (S * rw + s * w) - 1)

 a = S*(rw+w), b = S*rw + s*w

delta s = s * (a-b) / b

IOW, trade one divide for two multiplies

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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