linux-kernel - [RFC PATCH 09/11] sched: Optimize the !power_savings_balance during find_busiest

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Date:	Wed, 25 Mar 2009 14:44:17 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	"Ingo Molnar" <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Vaidyanathan Srinivasan" <svaidy@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	"Balbir Singh" <balbir@...ibm.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	"Dhaval Giani" <dhaval@...ux.vnet.ibm.com>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: [RFC PATCH 09/11] sched: Optimize the !power_savings_balance during
	find_busiest_group.

We don't need to perform power_savings balance if either the cpu is NOT_IDLE
or if the sched_domain doesn't contain the SD_POWERSAVINGS_BALANCE flag set.

Currently, we check for these conditions multiple number of times, even though
these variables don't change over the scope of find_busiest_group().

Check once, and store the value in the already exiting "power_savings_balance"
variable.

Signed-off-by: Gautham R Shenoy <ego@...ibm.com>
---

 kernel/sched.c |   23 ++++++++++++++---------
 1 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index b1b1b8a..cb2c97b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3282,8 +3282,17 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 	int load_idx;
 
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-	sds->power_savings_balance = 1;
-	sds->min_nr_running = ULONG_MAX;
+	/*
+	 * Busy processors will not participate in power savings
+	 * balance.
+	 */
+	if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+		sds->power_savings_balance = 0;
+	else {
+		sds->power_savings_balance = 1;
+		sds->min_nr_running = ULONG_MAX;
+		sds->leader_nr_running = 0;
+	}
 #endif
 	load_idx = get_sd_load_idx(sd, idle);
 
@@ -3318,12 +3327,8 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 		}
 
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-		/*
-		 * Busy processors will not participate in power savings
-		 * balance.
-		 */
-		if (idle == CPU_NOT_IDLE ||
-				!(sd->flags & SD_POWERSAVINGS_BALANCE))
+
+		if (!sds->power_savings_balance)
 			goto group_next;
 
 		/*
@@ -3547,7 +3552,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 
 out_balanced:
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-	if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+	if (!sds.power_savings_balance)
 		goto ret;
 
 	if (sds.this != sds.group_leader || sds.group_leader == sds.group_min)

--
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