linux-kernel - Re: [PATCH RFC 1/5] sched,numa: build table of node hop distance

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Date:	Tue, 14 Oct 2014 03:49:52 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, mgorman@...e.de, chegu_vinod@...com,
	mingo@...nel.org, efault@....de, vincent.guittot@...aro.org
Subject: Re: [PATCH RFC 1/5] sched,numa: build table of node hop distance

On 10/14/2014 02:47 AM, Peter Zijlstra wrote:
> On Sun, Oct 12, 2014 at 09:28:04AM -0400, Rik van Riel wrote:
>> On 10/12/2014 09:17 AM, Peter Zijlstra wrote:
>>> On Wed, Oct 08, 2014 at 03:37:26PM -0400, riel@...hat.com wrote:
>>>> +	sched_domains_numa_hops = kzalloc(sizeof(int) * nr_node_ids * nr_node_ids, GFP_KERNEL);
>>>> +	if (!sched_domains_numa_hops)
>>>> +		return;
>>>
>>> That's potentially a _BIG_ table (1M for a 512 node system).
>>> The node_distance has magic allocations and is of u8 size, is there any
>>> way we can re-use node_distance and avoid a second O(n^2) allocation?
>>
>> You are right, this should be a u8 at the least.
>>
>> Beyond that, I am not convinced that merging things into
>> the same array is worthwhile, since (IIRC) nr_node_ids
>> should be set to the actual number of nodes on the system
>> by then.
>
> The thing is, it looks like all you do is compare hop distance, and the
> order of the hop distances is the exact same order as the regular numa
> distance. I could not find a place where you use the actual hop value.

I use the actual hop distances when doing the scoring
for glueless mesh topologies, in patch 4/5.

> So if all you're interested in is the relative ordering, that should be
> the same for both.
>

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