From mboxrd@z Thu Jan  1 00:00:00 1970
From: George Dunlap <george.dunlap@eu.citrix.com>
Subject: Re: [PATCH 1/2] x86: during boot,
 anticipate identifying the boot cpu
Date: Mon, 1 Sep 2014 16:12:06 +0100
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To: Jan Beulich <JBeulich@suse.com>, Dario Faggioli <dario.faggioli@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, keir@xen.org, xen-devel <xen-devel@lists.xenproject.org>
List-Id: xen-devel@lists.xenproject.org

On 08/25/2014 09:39 AM, Jan Beulich wrote:
>>>> On 22.08.14 at 19:15, <dario.faggioli@citrix.com> wrote:
>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -1262,6 +1262,12 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>>   
>>       timer_init();
>>   
>> +    /*
>> +     * Identify the boot CPU, in case the scheduler initialization
>> +     * needs to know about it (e.g., topology, etc.)
>> +     */
>> +    identify_cpu(&boot_cpu_data);
>> +
>>       init_idle_domain();
>>   
>>       trap_init();
>> @@ -1272,8 +1278,6 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>>   
>>       arch_init_memory();
>>   
>> -    identify_cpu(&boot_cpu_data);
>> -
>>       if ( cpu_has_fxsr )
>>           set_in_cr4(X86_CR4_OSFXSR);
>>       if ( cpu_has_xmm )
> I'm not sure about this part: It currently makes quite a bit of sense
> to have identify_cpu() immediately before explicit users of the
> gathered data (all code following up to the alternative_instructions()
> call). Perhaps if you move identify_cpu(), all the others should get
> moved too?

Or possibly, move init_idle_domain() until after?  I took a quick look 
through the functions called between init_idle_domain() and 
identify_cpu(), and didn't see any dependencies on the idle domain or 
scheduling functions.  It's quite possible I missed something though.

Overall I think this approach looks good, and I agree with the comments 
already given.

  -George