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

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Date:	Wed, 22 Feb 2012 17:02:59 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"Brown, Len" <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

Konrad Rzeszutek Wilk wrote:
> 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.

I'm OK with x86_init approach, but advantage of 'config ACPI_PROCESSOR_AGGREGATOR as bool' would get rid of X86/IA64/... arch issue for xen (at least from coding view), through it need disable native acpi_pad module (IMO acpi_pad module has not strong reason to must be so).
Have a re-consider of this approach? :-)

Thanks,
Jinsong

>> 
>> 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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