linux-kernel - Re: [PATCH v3 6/7] x86/smpboot: introduce per-cpu variable for HT siblings

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Date:   Thu, 27 Jun 2019 08:54:49 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     subhra mazumdar <subhra.mazumdar@...cle.com>
cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, steven.sistare@...cle.com,
        dhaval.giani@...cle.com, daniel.lezcano@...aro.org,
        vincent.guittot@...aro.org, viresh.kumar@...aro.org,
        tim.c.chen@...ux.intel.com, mgorman@...hsingularity.net
Subject: Re: [PATCH v3 6/7] x86/smpboot: introduce per-cpu variable for HT
 siblings

On Thu, 27 Jun 2019, Thomas Gleixner wrote:

> On Wed, 26 Jun 2019, subhra mazumdar wrote:
> 
> > Introduce a per-cpu variable to keep the number of HT siblings of a cpu.
> > This will be used for quick lookup in select_idle_cpu to determine the
> > limits of search.
> 
> Why? The number of siblings is constant at least today unless you play
> silly cpu hotplug games. A bit more justification for adding yet another
> random storage would be appreciated.
> 
> > This patch does it only for x86.
> 
> # grep 'This patch' Documentation/process/submitting-patches.rst
> 
> IOW, we all know already that this is a patch and from the subject prefix
> and the diffstat it's pretty obvious that this is x86 only.
> 
> So instead of documenting the obvious, please add proper context to justify
> the change.

Aside of that the right ordering is to introduce the default fallback in a
separate patch, which explains the reasoning and then in the next one add
the x86 optimized version.

Thanks,

	tglx