linux-kernel - Re: [PATCH v2 2/5] sched/numa: Replace runnable_load_avg by load

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Message-ID: <e28bb567-dade-877b-f338-ce87e28cc02d@arm.com>
Date:   Tue, 18 Feb 2020 16:50:48 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        linux-kernel@...r.kernel.org, pauld@...hat.com,
        parth@...ux.ibm.com, hdanton@...a.com
Subject: Re: [PATCH v2 2/5] sched/numa: Replace runnable_load_avg by load_avg

On 18/02/2020 15:38, Mel Gorman wrote:
>>
>> Could we reuse group_type instead? The definitions are the same modulo
>> s/group/node/.
>>
> 
> I kept the naming because there is the remote possibility that NUMA
> balancing will deviate in some fashion. Right now, it's harmless.
> 

Since it's just a subset ATM I'd go for the reuse and change that later if
shown a split is required, but fair enough.

> I didn't merge that part of the first version of my series. I was
> waiting to see how the implementation for allowing a small degree of
> imbalance looks like. If it's entirely confined in adjust_numa_balance
                                                     ^^^^^^^^^^^^^^^^^^^
Apologies if that's a newbie question, but I'm not familiar with that one.
Would that be added in your reconciliation series? I've only had a brief
look at it yet (it's next on the chopping block).

> then I'll create the common helper at the same time. For now, I left the
> possibility open that numa_classify would use something different than
> group_is_overloaded or group_has_capacity even if I find that hard to
> imagine at the moment.
> 
>> What I'm naively thinking here is that we could have either move the whole
>> thing to just sg_lb_stats (AFAICT the fields of numa_stats are a subset of it),
>> or if we really care about the stack we could tweak the ordering to ensure
>> we can cast one into the other (not too enticed by that one though).
>>
> 
> Yikes, no I'd rather not do that. Basically all I did before was create
> a common helper like __lb_has_capacity that only took basic types as
> parameters. group_has_capacity and numa_has_capacity were simple wrappers
> that read the correct fields from their respective stats structures.
> 

That's more sensible indeed. It'd definitely be nice to actually reconcile
the two balancers with these common helpers, though I guess it doesn't
*have* to happen with this very patch.