linux-kernel - [RFC PATCH v2 5/7] sched: nominate preferred wakeup cpu

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Message-ID: <20080908132132.3221.6102.stgit@drishya.in.ibm.com>
Date:	Mon, 08 Sep 2008 18:51:32 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	David Collier-Brown <davecb@....com>,
	Tim Connors <tconnors@...ro.swin.edu.au>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: [RFC PATCH v2 5/7] sched: nominate preferred wakeup cpu

When the system utilisation is low and more cpus are idle,
then the process waking up from sleep should prefer to
wakeup an idle cpu from semi-idle cpu package (multi core
package) rather than a completely idle cpu package which
would waste power.

Use the sched_mc balance logic in find_busiest_group() to
nominate a preferred wakeup cpu.

This info can be sored in appropriate sched_domain, but
updating this info in all copies of sched_domain is not
practical.  For now lets try with a global variable.

Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
---

 kernel/sched.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 569fc8d..4ae79f5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3380,6 +3380,9 @@ out_balanced:
 
 	if (this == group_leader && group_leader != group_min) {
 		*imbalance = min_load_per_task;
+		if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP)
+			sched_mc_preferred_wakeup_cpu =
+					first_cpu(group_leader->cpumask);
 		return group_min;
 	}
 #endif
@@ -6911,6 +6914,13 @@ static void sched_domain_node_span(int node, cpumask_t *span)
 int sched_smt_power_savings = 0, sched_mc_power_savings = 0;
 
 /*
+ * Preferred wake up cpu nominated by sched_mc balance that will be used when
+ * most cpus are idle in the system indicating overall very low system
+ * utilisation. Triggered at POWERSAVINGS_BALANCE_WAKEUP (2).
+ */
+unsigned int sched_mc_preferred_wakeup_cpu;
+
+/*
  * SMT sched-domains:
  */
 #ifdef CONFIG_SCHED_SMT

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