linux-kernel - Re: [PATCH x86/mm UPDATED] x86-64, NUMA: Fix distance table handling

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Date:	Fri, 11 Mar 2011 10:25:23 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	David Rientjes <rientjes@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	tglx@...utronix.de, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH x86/mm UPDATED] x86-64, NUMA: Fix distance table handling

On Fri, Mar 11, 2011 at 10:19 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Fri, Mar 11, 2011 at 10:02:41AM -0800, Yinghai Lu wrote:
>> > No, NUMA implementation can skip numa_set_distance() entirely if the
>> > distance is LOCAL_DISTANCE if nids are equal, REMOTE_DISTANCE
>> > otherwise.  In fact, any amdtopology configuraiton would behave this
>> > way, so it's incorrect to fill the table with LOCAL_DISTANCE.  You
>> > have to check the physnid mapping and build new table whether physical
>> > table exists or not.  Lack of physical distance table doesn't mean all
>> > nodes are LOCAL_DISTANCE.
>>
>> too bad. We should call numa_alloc_distance in amdtopology to set
>> default value in that array.
>
> I'm not following.  If there's no distance table, the distance is
> assumed to be LOCAL between the same node and REMOTE if the nodes are
> different, which is exactly the way it should be for those machines.
> Why is this bad and why would you allocate distance table for such
> configurations?

now even emulation have that distance array.

why keep it simple to make all path have that array?

Yinghai
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