linux-kernel - Re: [Xen-devel] [PATCH 1/3] PAD helper for native and paravirt platform

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Date:	Tue, 21 Feb 2012 09:27:24 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Liu, Jinsong" <jinsong.liu@...el.com>, lenb@...nel.org,
	len.brown@...el.com
Cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"keir.xen@...il.com" <keir.xen@...il.com>,
	Jan Beulich <JBeulich@...e.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"lenb@...nel.org" <lenb@...nel.org>
Subject: Re: [Xen-devel] [PATCH 1/3] PAD helper for native and paravirt
 platform

On Tue, Feb 21, 2012 at 05:49:58AM +0000, Liu, Jinsong wrote:
> Konrad Rzeszutek Wilk wrote:
> >>>>> +struct pv_pad_ops {
> >>>>> +	int (*acpi_pad_init)(void);
> >>>>> +	void (*acpi_pad_exit)(void);
> >>>>> +};
> >>>>> +
> >>> 
> >>> Looking at this a bit closer I am not sure why you choose the
> >>> paravirt interface for this? There is another one - the x86 that
> >>> could have been choosen. Or introduce a new one that is specific to
> >>> ACPI. 
> >>> 
> >>> I am curious - what was the reason for using the paravirt interface?
> >>> I understand it does get the job done, but it seems a bit overkill
> >>> when something simple could have been used?
> >>> 
> >> 
> >> It uses paravirt interface to avoid some code like 'xen_...' in
> >> native code path (acpi_pad.c). 
> >> I'm not quite sure what does 'x86' here mean? Adding 2 fields
> >> (acpi_pad_init/exit) in arch/x86/xen/enlighten.c --> xen_cpu_ops?
> >> seems it's much simpler.  
> > 
> > arch/x86/include/asm/x86_init.h
> > 
> > But before you go that way let me ask you another question - can ACPI
> > PAD 
> > be used on ARM or IA64? If so, wouldn't this fail compilation as this
> > pvops structure is not defined on IA64?
> 
> Ideally ACPI PAD is not bound to some arch, so IMO it could be used at least on IA64 (through currently no real PAD on IA64 platform as far as I know).
> However, in native acpi_pad implementation, it indeed depends on X86 for reason like mwait.
> So for xen acpi_pad, I think it's OK to choose x86, defining an acpi_pad_ops at x86_init.c which would be overwritten when xen init.

OK, or in osl.c. We need Len to chime in here as I can see this expanding in the future.
> 
> Another choice is to define config ACPI_PROCESSOR_AGGREGATOR as 'bool', which would disable native acpi_pad module.

Ewww. No.
> 
> Your opinion?
> 
> Thanks,
> Jinsong
> 
> > 
> > The other thing I am not comfortable about is that the pvops structure
> > are used for low-level code. Not for higher up, like ACPI. For that
> > another structure seems more prudent. Perhaps something like the x86
> > one, but specific to ACPI?
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