linux-kernel - Re: [PATCH v2 4/4] sched:Use correct nid while evaluating task weights

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Date:	Tue, 16 Jun 2015 11:00:18 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v2 4/4] sched:Use correct nid while evaluating task weights

On 06/16/2015 07:56 AM, Srikar Dronamraju wrote:
> In task_numa_migrate(), while evaluating other nodes for group
> consolidation, env.dst_nid is used instead of using the iterator nid.
> Using env.dst_nid would mean dist is always the same. Infact the same
> dist was calculated above while evaluating the preferred node.
> 
> Fix the above to use the iterator nid.

Good catch.

> Also the task/group weights from the src_nid should be calculated
> irrespective of numa topology type.

If you look at score_nearby_nodes(), you will see that
maxdist is only used when the topology is NUMA_BACKPLANE.

The source score never changes when having a directly
connected or NUMA_GLUELESS_MESH type system, so the source
score does not need to be recalculated unless we are actually
dealing with a NUMA_BACKPLANE topology.

Looking forward to a v2 with just the first fix.

> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> ---
>  kernel/sched/fair.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d1aa374..e1b3393 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1493,9 +1493,8 @@ static int task_numa_migrate(struct task_struct *p)
>  			if (nid == env.src_nid || nid == p->numa_preferred_nid)
>  				continue;
>  
> -			dist = node_distance(env.src_nid, env.dst_nid);
> -			if (sched_numa_topology_type == NUMA_BACKPLANE &&
> -						dist != env.dist) {
> +			dist = node_distance(env.src_nid, nid);
> +			if (dist != env.dist) {
>  				taskweight = task_weight(p, env.src_nid, dist);
>  				groupweight = group_weight(p, env.src_nid, dist);
>  			}
> 

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