Messages in this thread Patch in this message | | | Date | Fri, 27 Jun 2008 13:41:32 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 23/30] sched: optimize effective_load() |
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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> --- kernel/sched_fair.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
Index: linux-2.6/kernel/sched_fair.c =================================================================== --- linux-2.6.orig/kernel/sched_fair.c +++ linux-2.6/kernel/sched_fair.c @@ -1079,16 +1079,16 @@ static unsigned long effective_load(stru 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 } --
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