linux-kernel - Re: [PATCH 2/4] sched,numa: weigh nearby nodes for task placement on complex NUMA topologies

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Date:	Fri, 09 May 2014 11:14:21 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, mingo@...nel.org, mgorman@...e.de,
	chegu_vinod@...com
Subject: Re: [PATCH 2/4] sched,numa: weigh nearby nodes for task placement
 on complex NUMA topologies

On 05/09/2014 05:53 AM, Peter Zijlstra wrote:
> On Thu, May 08, 2014 at 01:23:29PM -0400, riel@...hat.com wrote:
>> +		/*
>> +		 * For nodes with distances in-between LOCAL_DISTANCE
>> +		 * and max_distance, we count the faults on those nodes
>> +		 * in proportion to their distance, using this formula:
>> +		 *
>> +		 * max_distance - node_distance
>> +		 * -----------------------------
>> +		 * max_distance - LOCAL_DISTANCE
>> +		 */
>> +		if (task)
>> +			faults = task_faults(p, node);
>> +		else
>> +			faults = group_faults(p, node);
>> +
>> +		score += 1000 * faults *
>> +				(max_distance - distance) /
>> +				(max_distance - LOCAL_DISTANCE);
>
> OK that makes sense, except I would suggest you use a power-of-two scale
> factor :-)

I guess we could build a NUMA distance table that
counts the number of hops, and use that.

That is likely to result in better/easier values
for grouping than the (somewhat arbitrary) distances
in the SLIT table, anyway...
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