From: Stephan Baerwolf Date: Wed, 11 May 2011 16:03:29 +0000 (+0200) Subject: sched: Fix and optimise calculation of the weight-inverse X-Git-Tag: v3.0-rc1~403^2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=db670dac49b5423b39b5e523d28fe32045d71b10;p=pandora-kernel.git sched: Fix and optimise calculation of the weight-inverse If the inverse loadweight should be zero, function "calc_delta_mine" calculates the inverse of "lw->weight" (in 32bit integer ops). This calculation is actually a little bit impure (because it is inverting something around "lw-weight"+1), especially when "lw->weight" becomes smaller. The correct inverse would be 1/lw->weight multiplied by "WMULT_CONST" for fixcomma-scaling it into integers. (So WMULT_CONST/lw->weight ...) The old, impure algorithm took two divisions for inverting lw->weight, the new, more exact one only takes one and an additional unlikely-if. Signed-off-by: Stephan Baerwolf Signed-off-by: Peter Zijlstra Cc: Linus Torvalds Link: http://lkml.kernel.org/n/tip-0pz0wnyalr4tk4ln11xwumdx@git.kernel.org [ This could explain some aritmetical issues for small shares but nothing concrete has been reported yet so we are not confident enough to queue this up in sched/urgent and for -stable backport. But if anyone finds this commit and sees it to fix some badness then we can certainly change our mind! ] Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed