linux-kernel - Re: [RFC PATCH v3 0/3] acpi: Introduce prepare

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Date:	Fri, 07 Dec 2012 00:52:26 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	Hanjun Guo <guohanjun@...wei.com>,
	Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>,
	linux-acpi@...r.kernel.org, isimatu.yasuaki@...fujitsu.com,
	wency@...fujitsu.com, rjw@...k.pl, lenb@...nel.org,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Tang Chen <tangchen@...fujitsu.com>
Subject: Re: [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation

On 12/07/2012 12:31 AM, Toshi Kani wrote:
> On Fri, 2012-12-07 at 00:25 +0800, Jiang Liu wrote:
>> On 12/07/2012 12:03 AM, Toshi Kani wrote:
>>> On Fri, 2012-12-07 at 00:00 +0800, Jiang Liu wrote:
>>>> On 11/29/2012 02:41 AM, Toshi Kani wrote:
>>>>> On Wed, 2012-11-28 at 19:05 +0800, Hanjun Guo wrote:
>  : 
>>>>> Yes, sharing idea is good. :)  I do not know if we need all 6 steps (I
>>>>> have not looked at all your changes yet..), but in my mind, a hot-plug
>>>>> operation should be composed with the following 3 phases.
>>>>>
>>>>> 1. Validate phase - Verify if the request is a supported operation.  All
>>>>> known restrictions are verified at this phase.  For instance, if a
>>>>> hot-remove request involves kernel memory, it is failed in this phase.
>>>>> Since this phase makes no change, no rollback is necessary to fail.  
>>>>>
>>>>> 2. Execute phase - Perform hot-add / hot-remove operation that can be
>>>>> rolled-back in case of error or cancel.
>>>>>
>>>>> 3. Commit phase - Perform the final hot-add / hot-remove operation that
>>>>> cannot be rolled-back.  No error / cancel is allowed in this phase.  For
>>>>> instance, eject operation is performed at this phase.  
>>>> Hi Toshi,
>>>> 	There are one more step needed. Linux provides sysfs interfaces to
>>>> online/offline CPU/memory sections, so we need to protect from concurrent
>>>> operations from those interfaces when doing physical hotplug. Think about
>>>> following sequence:
>>>> Thread 1
>>>> 1. validate conditions for hot-removal
>>>> 2. offline memory section A
>>>> 3.						online memory section A			
>>>> 4. offline memory section B
>>>> 5 hot-remove memory device hosting A and B.
>>>
>>> Hi Gerry,
>>>
>>> I agree.  And I am working on a proposal that tries to address this
>>> issue by integrating both sysfs and hotplug operations into a framework.
>> Hi Toshi,
>> 	But the sysfs for CPU and memory online/offline are platform independent
>> interfaces, and the ACPI based hotplug is platform dependent interfaces. I'm not
>> sure whether it's feasible to merge them. For example we still need offline interface
>> to stop using faulty CPUs on platform without physical hotplug capabilities.
>> 	We have solved this by adding a "busy" flag to the device, so the sysfs
>> will just return -EBUSY if the busy flag is set.
> 
> I am making the framework code platform-independent so that it can
> handle both cases.  Well, I am still prototyping, so hopefully it will
> work. :)
Do you mean implementing a framework to manage hotplug of any type of devices?
That sounds like a huge plan:)

Otherwise there may be a gap. CPU online/offline interface deals with logical
CPU, and hotplug driver deals with physical devices(processor). They may be different
by related objects.

> 
> Thanks,
> -Toshi
> 

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