[RFC/PATCH 11/17] sched: fair: optimize sched_slice()

[Peter Zijlstra]

Cache the divide in the hope we can avoid doing it in steady state opteration.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
 kernel/sched.c       |    2 ++
 kernel/sched_debug.c |    1 +
 kernel/sched_fair.c  |    6 ++----
 3 files changed, 5 insertions(+), 4 deletions(-)

Index: linux-2.6-2/kernel/sched.c
===================================================================
--- linux-2.6-2.orig/kernel/sched.c
+++ linux-2.6-2/kernel/sched.c
@@ -1298,11 +1298,13 @@ calc_delta_mine(unsigned long delta_exec
 static inline void update_load_add(struct load_weight *lw, unsigned long inc)
 {
 	lw->weight += inc;
+	lw->inv_weight = 0;
 }
 
 static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
 {
 	lw->weight -= dec;
+	lw->inv_weight = 0;
 }
 
 /*
Index: linux-2.6-2/kernel/sched_debug.c
===================================================================
--- linux-2.6-2.orig/kernel/sched_debug.c
+++ linux-2.6-2/kernel/sched_debug.c
@@ -137,6 +137,7 @@ void print_cfs_rq(struct seq_file *m, in
 			SPLIT_NS(spread0));
 	SEQ_printf(m, "  .%-30s: %ld\n", "nr_running", cfs_rq->nr_running);
 	SEQ_printf(m, "  .%-30s: %ld\n", "load", cfs_rq->load.weight);
+	SEQ_printf(m, "  .%-30s: %ld\n", "load^-1", cfs_rq->load.inv_weight);
 #ifdef CONFIG_SCHEDSTATS
 	SEQ_printf(m, "  .%-30s: %d\n", "bkl_count",
 			rq->bkl_count);
Index: linux-2.6-2/kernel/sched_fair.c
===================================================================
--- linux-2.6-2.orig/kernel/sched_fair.c
+++ linux-2.6-2/kernel/sched_fair.c
@@ -369,10 +369,8 @@ static u64 sched_slice(struct cfs_rq *cf
 		goto out;
 
 	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
-
-		slice *= se->load.weight;
-		do_div(slice, cfs_rq->load.weight);
+		slice = calc_delta_mine(slice,
+				se->load.weight, &cfs_rq_of(se)->load);
 	}
 
 out:

--

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