linux-kernel - Re: [PATCH] arch/x86: Remove second call to topology_update_package

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Message-ID: <57FEBB22.6090601@redhat.com>
Date:   Wed, 12 Oct 2016 18:37:22 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>, linux-kernel@...r.kernel.org
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <len.brown@...el.com>, Borislav Petkov <bp@...e.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] arch/x86: Remove second call to topology_update_package_map()



On 10/12/2016 06:06 PM, Tim Chen wrote:
> On Wed, 2016-10-12 at 16:54 -0400, Prarit Bhargava wrote:
>>
>> On 10/12/2016 03:51 PM, Tim Chen wrote:
>>>
>>> On Wed, 2016-10-12 at 11:06 -0400, Prarit Bhargava wrote:
>>>>
>>>>
>>>> On 10/12/2016 10:36 AM, Prarit Bhargava wrote:
>>>>>
>>>>>
>>>>> This was noticed during the investigation of
>>>>>
>>>>> http://git.kernel.org/tip/2a51fe083eba7f99cbda72f5ef90cdf2f4df882c
>>>>>
>>>>> A note for reviewers on the cleanup in smp_init_package_map(): The
>>>>> per_cpu variable x86_bios_cpu_apicid is initialized to BAD_APICID, and the
>>>>> bitmaps are set to false by default so the code isn't necessary.  The
>>>>> pr_warn() can also be dropped as generic_processor_info() will do a
>>>>> pr_warning() in the same situation.
>>>>>
>>>>>
>>>>>
>>>>> P.
>>>>>
>>>>> -----8<-----
>>>>>
>>>>> After commit 1f12e32f4cd5 ("x86/topology: Create logical package id"),
>>>>> topology_update_package_map() is called twice on a CPU.  The first call is in
>>>>> generic_processor_info(), which is called on all present cpus (found in either
>>>>> mptable or ACPI MADT).  The second call is in smp_init_package_map() which
>>>>> is called later on in the init sequence.
>>>>>
>>>>> Only a single call is necessary for the kernel to initialize the data
>>>>> structures properly. This patch drops the later call in smp_init_package_map()
>>>>> and moves smp_init_package_map() out of smp_store_boot_cpu_info().
>>>>>
>>>> Self-NAK.
>>>>
>>>> This seems to not work on systems with an empty socket :/.  Looking into this now.
>>>>
>>>> P.
>>> My single node workstation also failed to boot with the patch.
>> The patch is incorrect.  I'm dropping it completely.
>>
> 
> The call from generic_processor_info to topology_update_package_map
> during early boot was essentially no op, as physical_package_map has
> not have been allocated by smp_init_package_map yet.
> 
> We have to call topology_update_package_map in smp_init_package_map
> after allocating physical_package_map to properly set up
> physical_package_map.

Right -- the patch is incorrect (see above).  I'm dropping it completely.

P.

> 
> Tim
>