From cb5ef42a03a13f95a9ea94e6cda4f7a47497871f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 27 Jun 2008 13:41:32 +0200 Subject: [PATCH] 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 Cc: Srivatsa Vaddagiri Cc: Mike Galbraith Signed-off-by: Ingo Molnar --- kernel/sched_fair.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index a1694441f8b7..0d197be3e3e9 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1082,16 +1082,16 @@ static unsigned long effective_load(struct task_group *tg, long wl, int cpu) for_each_sched_entity(se) { #define D(n) (likely(n) ? (n) : 1) - long S, Srw, rw, s, sn; + long S, rw, s, a, b; S = se->my_q->tg->shares; s = se->my_q->shares; rw = se->my_q->load.weight; - Srw = S * rw / D(s); - sn = S * (rw + wl) / D(Srw + wg); + a = S*(rw + wl); + b = S*rw + s*wg; - wl = sn - s; + wl = s*(a-b)/D(b); wg = 0; #undef D } -- 2.30.2