Date: Fri, 19 Dec 2008 13:55:08 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, suresh.b.siddha@intel.com,
       venkatesh.pallipadi@intel.com, a.p.zijlstra@chello.nl, mingo@elte.hu,
       dipankar@in.ibm.com, balbir@linux.vnet.ibm.com,
       vatsa@linux.vnet.ibm.com, ego@in.ibm.com, andi@firstfloor.org,
       davecb@sun.com, tconnors@astro.swin.edu.au, maxk@qualcomm.com,
       gregory.haskins@gmail.com, pavel@suse.cz, svaidy@linux.vnet.ibm.com,
       Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH v7 4/8] sched: nominate preferred wakeup cpu
Message-Id: <20081219135508.9c6217ba.akpm@linux-foundation.org>
In-Reply-To: <20081218175622.29812.69201.stgit@drishya.in.ibm.com>
References: <20081218175313.29812.4781.stgit@drishya.in.ibm.com>
	<20081218175622.29812.69201.stgit@drishya.in.ibm.com>
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On Thu, 18 Dec 2008 23:26:22 +0530
Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> wrote:

> 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.
> 

kernel/sched.c: In function 'find_busiest_group':
kernel/sched.c:3403: warning: passing argument 1 of '__first_cpu' from incompatible pointer type

Due to

	first_cpu(group_leader->cpumask);

apparently because Rusty changed sched_group.cpumask into a plain old
array and nobody tests their stuff against the tree into which it is
actually integrated :(

kernel/sched.c: In function 'schedule':
kernel/sched.c:3679: warning: 'active_balance' may be used uninitialized in this function

This warning is correct - the code is buggy.
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