linux-kernel - [PATCH v3 2/3] sched: scale the busy and this queue's per-task load before compare

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Date:	Tue, 18 Jun 2013 11:18:05 +0800
From:	Lei Wen <leiwen@...vell.com>
To:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	<mingo@...hat.com>, <leiwen@...vell.com>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v3 2/3] sched: scale the busy and this queue's per-task load before compare

Since for max_load and this_load, they are the value that already be
scaled. It is not reasonble to get a minimum value between the scaled
and non-scaled value, like below example.
	min(sds->busiest_load_per_task, sds->max_load);

Also add comment over in what condition, there would be cpu power gain
in move the load.

Signed-off-by: Lei Wen <leiwen@...vell.com>
---
 kernel/sched/fair.c |   38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 28052fa..6173095 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4692,10 +4692,14 @@ void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
 {
 	unsigned long tmp, pwr_now = 0, pwr_move = 0;
 	unsigned int imbn = 2;
-	unsigned long scaled_busy_load_per_task;
 
 	if (sds->this_nr_running) {
 		sds->this_load_per_task /= sds->this_nr_running;
+
+		/* Scale this_load_per_task to local power not related */
+		sds->this_load_per_task <<= SCHED_POWER_SHIFT;
+		sds->this_load_per_task /= sds->this->sgp->power;
+
 		if (sds->busiest_load_per_task >
 				sds->this_load_per_task)
 			imbn = 1;
@@ -4704,12 +4708,8 @@ void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
 			cpu_avg_load_per_task(env->dst_cpu);
 	}
 
-	scaled_busy_load_per_task = sds->busiest_load_per_task
-					 * SCHED_POWER_SCALE;
-	scaled_busy_load_per_task /= sds->busiest->sgp->power;
-
-	if (sds->max_load - sds->this_load + scaled_busy_load_per_task >=
-			(scaled_busy_load_per_task * imbn)) {
+	if (sds->max_load - sds->this_load + sds->busiest_load_per_task >=
+			(sds->busiest_load_per_task * imbn)) {
 		env->imbalance = sds->busiest_load_per_task;
 		return;
 	}
@@ -4727,22 +4727,29 @@ void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
 	pwr_now /= SCHED_POWER_SCALE;
 
 	/* Amount of load we'd subtract */
-	if (sds->max_load > scaled_busy_load_per_task) {
+	if (sds->max_load > sds->busiest_load_per_task) {
 		pwr_move += sds->busiest->sgp->power *
 			min(sds->busiest_load_per_task,
-				sds->max_load - scaled_busy_load_per_task);
-		tmp = (sds->busiest_load_per_task * SCHED_POWER_SCALE) /
-			sds->this->sgp->power;
+				sds->max_load - sds->busiest_load_per_task);
+		tmp = sds->busiest_load_per_task;
 	} else
-		tmp = (sds->max_load * sds->busiest->sgp->power) /
-			sds->this->sgp->power;
+		tmp = sds->max_load;
 
+	/* Scale to this queue from busiest queue */
+	tmp = (tmp * sds->busiest->sgp->power) /
+		sds->this->sgp->power;
 	/* Amount of load we'd add */
 	pwr_move += sds->this->sgp->power *
 			min(sds->this_load_per_task, sds->this_load + tmp);
 	pwr_move /= SCHED_POWER_SCALE;
 
 	/* Move if we gain throughput */
+	/*
+	 * The only possibilty for below statement be true, is:
+	 * sds->max_load is larger than sds->busiest_load_per_task, while,
+	 * sds->busiest_load_per_task is larger than sds->this_load plus by
+	 * the scaled sds->busiest_load_per_task moved into this queue
+	 */
 	if (pwr_move > pwr_now)
 		env->imbalance = sds->busiest_load_per_task;
 }
@@ -4758,6 +4765,11 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 	unsigned long max_pull, load_above_capacity = ~0UL;
 
 	sds->busiest_load_per_task /= sds->busiest_nr_running;
+
+	/* Scale busiest_load_per_task to local power not related */
+	sds->busiest_load_per_task <<= SCHED_POWER_SHIFT;
+	sds->busiest_load_per_task /= sds->busiest->sgp->power;
+
 	if (sds->group_imb) {
 		sds->busiest_load_per_task =
 			min(sds->busiest_load_per_task, sds->avg_load);
-- 
1.7.10.4

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