From: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Subject: [PATCH v7 4/8] sched: nominate preferred wakeup cpu
To: Linux Kernel <linux-kernel@vger.kernel.org>,
        Suresh B Siddha <suresh.b.siddha@intel.com>,
        Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>, Dipankar Sarma <dipankar@in.ibm.com>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Vatsa <vatsa@linux.vnet.ibm.com>, Gautham R Shenoy <ego@in.ibm.com>,
        Andi Kleen <andi@firstfloor.org>, David Collier-Brown <davecb@sun.com>,
        Tim Connors <tconnors@astro.swin.edu.au>,
        Max Krasnyansky <maxk@qualcomm.com>,
        Gregory Haskins <gregory.haskins@gmail.com>,
        Pavel Machek <pavel@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Date: Thu, 18 Dec 2008 23:26:22 +0530
Message-ID: <20081218175622.29812.69201.stgit@drishya.in.ibm.com>
In-Reply-To: <20081218175313.29812.4781.stgit@drishya.in.ibm.com>
References: <20081218175313.29812.4781.stgit@drishya.in.ibm.com>
User-Agent: StGIT/0.14.2
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org

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.  Hence this information is stored in root_domain
struct which is one copy per partitioned sched domain.
The root_domain can be accessed from each cpu's runqueue
and there is one copy per partitioned sched domain.

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

 kernel/sched.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 0b9bbbd..3415fa3 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -493,6 +493,14 @@ struct root_domain {
 #ifdef CONFIG_SMP
 	struct cpupri cpupri;
 #endif
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+	/*
+	 * 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;
+#endif
 };
 
 /*
@@ -3407,6 +3415,10 @@ out_balanced:
 
 	if (this == group_leader && group_leader != group_min) {
 		*imbalance = min_load_per_task;
+		if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
+			cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
+					first_cpu(group_leader->cpumask);
+		}
 		return group_min;
 	}
 #endif

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/