linux-kernel - [PATCH 3/3] sched: Fix sd_parent_degenerate for SD_POWERSAVINGS

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Message-ID: <20090216165116.12804.90036.stgit@sofia.in.ibm.com>
Date:	Mon, 16 Feb 2009 22:21:16 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	linux-kernel@...r.kernel.org, svaidy@...ux.vnet.ibm.com,
	mingo@...e.hu, a.p.zijlstra@...llo.nl, suresh.b.siddha@...el.com,
	ego@...ibm.com
Cc:	balbir@...ibm.com, dipankar@...ibm.com, efault@....de,
	andi@...stfloor.org, Gautham R Shenoy <ego@...ibm.com>
Subject: [PATCH 3/3] sched: Fix sd_parent_degenerate for
	SD_POWERSAVINGS_BALANCE.

Currently a sched_domain having a single group can be prevented from getting
degenerated if it contains a SD_POWERSAVINGS_BALANCE flag. But since it has
only one group, it won't have any scope for performing powersavings balance as
it does not have a sibling group to pull from.

Apart from not provide any powersavings, it also fails to participate
in normal load-balancing.

Fix this by allowing such a sched_domain to degenerate and pass on the
responsibility of performing the POWERSAVINGS_BALANCE to it's parent domain.

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

 kernel/sched.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index af88f5a..32858fd 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6934,6 +6934,17 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
 				SD_SHARE_PKG_RESOURCES);
 		if (nr_node_ids == 1)
 			pflags &= ~SD_SERIALIZE;
+
+		/*
+		 * If the only flag that is preventing us from degenerating
+		 * a domain with a single group is power_savings balance,
+		 * see if we can transfer that responsibility to the new parent
+		 */
+		if (pflags & SD_POWERSAVINGS_BALANCE && parent->parent) {
+			pflags &= ~SD_POWERSAVINGS_BALANCE;
+			parent->parent->flags |=
+				sd_power_saving_flags(parent->level);
+		}
 	}
 	if (~cflags & pflags)
 		return 0;

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