linux-kernel - Re: [PATCH 3/5] X86/XEN: Introduce the x86_init.paging.pagetable

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Date:	Tue, 21 Aug 2012 21:26:17 +0100
From:	Attilio Rao <attilio.rao@...rix.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH 3/5] X86/XEN: Introduce the x86_init.paging.pagetable_init
 PVOPS

On 21/08/12 16:44, Thomas Gleixner wrote:
> On Tue, 21 Aug 2012, Attilio Rao wrote:
>
>    
>> This new PVOPS is responsible to setup the kernel pagetables and
>> replace entirely x86_init.paging.pagetable_setup_start and
>> x86_init.paging.pagetable_setup_done PVOPS work.
>>      
>
>    
>> For performance the x86_64 stub is implemented as a macro to paging_init()
>> rather than an actual function stub.
>>      
> Huch, using a macro for an once per boot time call is really a massive
> performance improvement.
>
> It's confusing and wrong. You just use a macro because x86_64 does not
> need any extra setups aside of paging_init().
>
>    
>> diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
>> index 849be14..c1e910a 100644
>> --- a/arch/x86/kernel/x86_init.c
>> +++ b/arch/x86/kernel/x86_init.c
>> @@ -68,6 +68,7 @@ struct x86_init_ops x86_init __initdata = {
>>   	},
>>
>>   	.paging = {
>> +		.pagetable_init		= native_pagetable_init,
>>      
> I'd prefer to see these patches implemented differently.
>
>   #1 Remove the base argument from pagetable_setup_start (leave
>      pagetable_setup_done() alone).
>
>   #2 Rename pagetable_setup_start to pagetable_init,
>      native_pagetable_setup_start to native_pagetable_init and
>      xen_pagetable_setup_start to xen_pagetable_init
>
>   #3 Instead of copying the whole native_pagetable_setup_start()
>      function and deleting it later, move the paging_init() call from
>      setup.c to native_pagetable_init() and xen_pagetable_init()
>      and define native_pagetable_init as paging_init() for x86_64
>
>   #4 Move the code from xen_pagetable_setup_done() into
>      xen_pagetable_init() and remove the now unused
>      pagetable_setup_done().
>
> That's less code shuffling and pointless copying which makes the
> review way easier.
>    

I've followed these steps in a new patch series (integrating suggestions 
from Konrad and Stefano too).

Attilio
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