linux-kernel - Re: [PATCH] x86/smpboot: Make logical package management more robust

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Message-ID: <20161208130434.GR3124@twins.programming.kicks-ass.net>
Date:   Thu, 8 Dec 2016 14:04:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        "Charles (Chas) Williams" <ciwillia@...cade.com>,
        "M. Vefa Bicakci" <m.v.b@...box.com>,
        Alok Kataria <akataria@...are.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH] x86/smpboot: Make logical package management more robust

On Thu, Dec 08, 2016 at 01:49:28PM +0100, Thomas Gleixner wrote:
> 
> > > -	if (logical_packages > __max_logical_packages) {
> > > -		pr_warn("Detected more packages (%u), then computed by BIOS data (%u).\n",
> > > -			logical_packages, __max_logical_packages);
> > > -		logical_packages_frozen = true;
> > > -		__max_logical_packages  = logical_packages;
> > 
> > So we'll never 'shrink' the initially computed max; which could result
> > in using more memory than strictly needed, otoh it makes physical
> > hotplug happier.
> 
> Yes. I was debating that back and forth and at the end decided that making
> it simple and robust is a good tradeoff vs. the slightly higher memory
> consumption. Though on most systems that's a non issue as number of
> possible cpus/packages is the same as the actual available ones. The insane
> setups have to suffer - rightfully so.

Don't we overestimate by a factor of 2 due to HT? That is, every single
socket Intel box will have a max_packages of 2.

Not that I care too deeply, and arguably the HT case _is_ insane because
its impossible to tell etc..