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Date: Fri, 10 Nov 2017 07:01:12 -0800
From: Andi Kleen <ak@linux.intel.com>
To: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@intel.com>, Piotr Luc <piotr.luc@intel.com>,
        Kan Liang <kan.liang@intel.com>, Borislav Petkov <bp@suse.de>,
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        Arvind Yadav <arvind.yadav.cs@gmail.com>,
        Andy Lutomirski <luto@kernel.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        He Chen <he.chen@linux.intel.com>,
        Mathias Krause <minipli@googlemail.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v5 2/3] x86/topology: Avoid wasting 128k for package id
 array
Message-ID: <20171110150112.GI8522@tassilo.jf.intel.com>
References: <20171105165428.32108-1-prarit@redhat.com>
 <20171105165428.32108-3-prarit@redhat.com>
 <alpine.DEB.2.20.1711071729270.1716@nanos>
 <372083ad-2a77-4646-bc67-dd4348a521d9@redhat.com>
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> > All of that works. There is no way to make sure that a lookup is fully
> > serialized against a concurrent update. Even if the lookup holds
> > cpu_read_lock() the new package might arrive right after the unlock.
> > 
> 
> Thanks Thomas.
> 
> Andi, do you want to take a look at this?

I was originally worried about races, that is why i tried to put 
everything into cpu_data. But that didn't work out because something
clears it. Perhaps the right solution would be some extra per_cpu
data variables, and search for the first match. I suspect that would
be simpler. But if that doesn't work I guess something like Thomas'
example will work.

I assume you will handle it, Prarit?

-Andi