linux-kernel - RE: [PATCH V1 1/2] Xen acpi memory hotplug driver

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Date:	Thu, 6 Dec 2012 04:27:36 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"lenb@...nel.org" <lenb@...nel.org>
Subject: RE: [PATCH V1 1/2] Xen acpi memory hotplug driver

>>>> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
>>>> index 126d8ce..abd0396 100644
>>>> --- a/drivers/xen/Kconfig
>>>> +++ b/drivers/xen/Kconfig
>>>> @@ -206,4 +206,15 @@ config XEN_MCE_LOG
>>>>  	  Allow kernel fetching MCE error from Xen platform and
>>>>  	  converting it into Linux mcelog format for mcelog tools
>>>> 
>>>> +config XEN_ACPI_MEMORY_HOTPLUG
>>>> +	bool "Xen ACPI memory hotplug"
>>> 
>>> There should be a way to make this a module.
>> 
>> I have some concerns to make it a module:
>> 1. xen and native memhotplug driver both work as module, while we
>> need early load xen driver. 
>> 2. if possible, a xen stub driver may solve load sequence issue, but
>>   it may involve other issues * if xen driver load then unload,
>> native driver may have chance to load successfully; 
> 
> The stub driver would still "occupy" the ACPI bus for the memory
> hotplug PnP, so I think this would not be a problem.
> 

I'm not quite clear your mean here, do you mean it has
1. xen_stub driver + xen_memhoplug driver, then xen_strub driver unload and entirely replaced by xen_memhotplug driver, or
2. xen_stub driver (w/ stub ops) + xen_memhotplug ops (not driver), then xen_stub driver keep occupying but its stub ops later replaced by xen_memhotplug ops?

If in way #1, it has risk that native driver may load (if xen driver unload).
If in way #2, xen_memhotplug ops lose the chance to probe/add/bind existed memory devices (since it's done when driver registerred).

>>   * if xen driver load --> unload --> load again, then it will lose
>> hotplug notification during unload period; 
> 
> Sure. But I think we can do it with this driver? After all the
> function of 
> it is to just tell the firmware to turn on/off sockets - and if we
> miss 
> one notification we won't take advantage of the power savings - but we
> can do that later on.
> 

Not only inform firmware.
Hotplug notify callback will invoke acpi_bus_add -> ... -> implicitly invoke drv->ops.add method to add the hotadded memory device.

> 
>>   * if xen driver load --> unload --> load again, then it will
>> re-add all memory devices, but the handle for 'booting memory
>> device' and 'hotplug memory device' are different while we have no
>> way to distinguish these 2 kind of devices.   
> 
> Wouldn't the stub driver hold onto that?
> 

Same question as comment #1. Do you mean it has a xen_stub driver (w/ stub ops) and a xen_memhotplug ops?

>> 
>> IMHO I think to make xen hotplug logic as module may involves
>> unexpected result. Is there any obvious advantages of doing so?
>> after all we have provided config choice to user. Thoughts?  
> 
> Yes, it becomes a module - which is what we want.
> 

What I meant here is, module will bring some unexpected issues for xen hotplug.
We can provide user 'bool' config choice, let them decide to build-in or not, but not 'tristate' choice.

Thanks
Jinsong--
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