linux-kernel - [RFC PATCH v1 2/2] sched: fix group_capacity for thread level consolidation

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Message-ID: <20120116162255.29759.6264.stgit@localhost>
Date:	Mon, 16 Jan 2012 21:52:55 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Indan Zupancic <indan@....nu>,
	Youquan Song <youquan.song@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH v1 2/2] sched: fix group_capacity for thread level
 consolidation

sched_powersavings for threaded systems need this fix for
consolidation to sibling threads to work.  Since threads have
fractional capacity, group_capacity will turn out to be one
always and not accommodate another task in the sibling thread.

This fix makes group_capacity a function of cpumask_weight that
will enable the power saving load balancer to pack tasks among
sibling threads and keep more cores idle.

Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
---
 kernel/sched/fair.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bae6ec8..c94e768 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4012,6 +4012,21 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 		 */
 		if (prefer_sibling && !local_group && sds->this_has_capacity)
 			sgs.group_capacity = min(sgs.group_capacity, 1UL);
+		/*
+		 * If power savings balance is set at this domain, then
+		 * make capacity equal to number of hardware threads to
+		 * accommodate more tasks until capacity is reached.
+		 */
+		else if (sd->flags & SD_POWERSAVINGS_BALANCE)
+			sgs.group_capacity =
+				cpumask_weight(sched_group_cpus(sg));
+
+			/*
+			 * The default group_capacity is rounded from sum of
+			 * fractional cpu_powers of sibling hardware threads
+			 * in order to enable fair use of available hardware
+			 * resources.
+			 */
 
 		if (local_group) {
 			sds->this_load = sgs.avg_load;

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