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

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Message-ID: <alpine.LFD.2.02.1208211722560.2856@ionos>
Date:	Tue, 21 Aug 2012 17:44:13 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Attilio Rao <attilio.rao@...rix.com>
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,
	x86@...nel.org, xen-devel@...ts.xensource.com
Subject: Re: [PATCH 3/5] X86/XEN: Introduce the x86_init.paging.pagetable_init
 PVOPS

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.

Thanks,

	tglx
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