linux-kernel - Re: [PATCH v3 1/2] sched: Create architecture specific sched domain distances

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Message-ID: <146f2f85affc35a735d5e035032d4e661be5507b.camel@linux.intel.com>
Date: Mon, 15 Sep 2025 13:04:32 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, 
 Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall
 <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,  Valentin Schneider	
 <vschneid@...hat.com>, Tim Chen <tim.c.chen@...el.com>, Vincent Guittot	
 <vincent.guittot@...aro.org>, Libo Chen <libo.chen@...cle.com>, Abel Wu	
 <wuyun.abel@...edance.com>, Len Brown <len.brown@...el.com>, 
	linux-kernel@...r.kernel.org, Chen Yu <yu.c.chen@...el.com>, K Prateek
 Nayak	 <kprateek.nayak@....com>, "Gautham R . Shenoy"
 <gautham.shenoy@....com>,  Zhao Liu <zhao1.liu@...el.com>, Vinicius Costa
 Gomes <vinicius.gomes@...el.com>, Arjan Van De Ven	
 <arjan.van.de.ven@...el.com>
Subject: Re: [PATCH v3 1/2] sched: Create architecture specific sched domain
 distances

On Mon, 2025-09-15 at 10:13 -0700, Tim Chen wrote:
> On Mon, 2025-09-15 at 14:37 +0200, Peter Zijlstra wrote:
> > On Thu, Sep 11, 2025 at 11:30:56AM -0700, Tim Chen wrote:

<snip>

> > > +
> > > +	if (sched_record_numa_dist(offline_node, numa_node_dist, &distances,
> > > +				   &nr_node_levels))
> > > +		return;
> > > +
> > > +	WRITE_ONCE(sched_avg_remote_numa_distance,
> > > +		   avg_remote_numa_distance(offline_node));
> > 
> > What is the point of all this? sched_avg_remote_numa_distance isn't
> > actually used anywhere. I'm thinking it doesn't want to be in this patch
> > at the very least.
> 
> sched_avg_remote_numa_distance actually could change when we offline/online a
> node.  I think arch_sched_node_distance(i, j) needs to be changed to
> arch_sched_node_distance(i, j, offline_node) so it knows not to include
> offline_node in its avg distance computation.  I will do that then.
> 

On second thought, GNR and CWF topology only need a remote average
distance.  Whether the offline node is entered into the computation
does not change the resulting sched domain topology.  So paasing
offline node is not necessary and I will update the code as such
and move the average distance computation to x86 specific file.

Tim