linux-kernel - Re: [PATCH 2/3 v3] x86/topology: Avoid wasting 128k for package id array

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Date:   Fri, 20 Oct 2017 11:03:03 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Prarit Bhargava <prarit@...hat.com>
cc:     linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Kan Liang <kan.liang@...el.com>, Borislav Petkov <bp@...e.de>,
        Stephane Eranian <eranian@...gle.com>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        He Chen <he.chen@...ux.intel.com>,
        Mathias Krause <minipli@...glemail.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 2/3 v3] x86/topology: Avoid wasting 128k for package id
 array

On Thu, 19 Oct 2017, Prarit Bhargava wrote:
>  static void remove_siblinginfo(int cpu)
>  {
> -	int sibling;
> +	int phys_pkg_id, sibling;
>  	struct cpuinfo_x86 *c = &cpu_data(cpu);
>  
>  	for_each_cpu(sibling, topology_core_cpumask(cpu)) {
> @@ -1529,6 +1526,12 @@ static void remove_siblinginfo(int cpu)
>  	cpumask_clear(topology_core_cpumask(cpu));
>  	c->phys_proc_id = 0;
>  	c->cpu_core_id = 0;
> +
> +	phys_pkg_id = c->phys_pkg_id;
> +	c->phys_pkg_id = U16_MAX;

This leaves c->logical_proc_set = 1, which is inconsistent at best. I have
no idea why we need this logical_proc_set flag at all.

> +	if (topology_phys_to_logical_pkg(phys_pkg_id) < 0)
> +		logical_packages--;

Now this has another issue. Depending on hotplug ordering the logical
package association can change across hotplug operations. I don't know it
that's an issue, but this needs to be analyzed before we merge that.

Thanks,

	tglx