linux-kernel - Re: [PATCH v6 2/7] sched: favour lower logical cpu number for sched

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Date:	Wed, 17 Dec 2008 23:39:32 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Dipankar Sarma <dipankar@...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>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Pavel Machek <pavel@...e.cz>
Subject: Re: [PATCH v6 2/7] sched: favour lower logical cpu number for
	sched_mc balance

* Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> [2008-12-17 22:56:42]:

> Just in case two groups have identical load, prefer to move load to lower
> logical cpu number rather than the present logic of moving to higher logical
> number.
> 
> find_busiest_group() tries to look for a group_leader that has spare capacity
> to take more tasks and freeup an appropriate least loaded group.  Just in case
> there is a tie and the load is equal, then the group with higher logical number
> is favoured.  This conflicts with user space irqbalance daemon that will move
> interrupts to lower logical number if the system utilisation is very low.
> 
> Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
> ---
> 
>  kernel/sched.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 16897ab..0b9bbbd 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -3264,7 +3264,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
>  		 */
>  		if ((sum_nr_running < min_nr_running) ||
>  		    (sum_nr_running == min_nr_running &&
> -		     first_cpu(group->cpumask) <
> +		     first_cpu(group->cpumask) >
>  		     first_cpu(group_min->cpumask))) {
>  			group_min = group;
>  			min_nr_running = sum_nr_running;
> @@ -3280,7 +3280,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
>  		if (sum_nr_running <= group_capacity - 1) {
>  			if (sum_nr_running > leader_nr_running ||
>  			    (sum_nr_running == leader_nr_running &&
> -			     first_cpu(group->cpumask) >
> +			     first_cpu(group->cpumask) <
>  			      first_cpu(group_leader->cpumask))) {
>  				group_leader = group;
>  				leader_nr_running = sum_nr_running;
> 
>

OK, so group_min is pushed to higher cpu numbers and group_leader is pulled to
lower cpu numbers

Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com> 

-- 
	Balbir
--
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