Re: [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation

[Jiang Liu <liuj97@gmail.com>]

On 12/07/2012 01:09 AM, Toshi Kani wrote:
> On Fri, 2012-12-07 at 00:52 +0800, Jiang Liu wrote:
>> 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.
> 
> Actually it is not a huge plan.  The framework I am thinking of is to
> enable a hotplug sequencer something analogous to do_initcalls() at the
> boot sequence.  I am not doing any huge re-work.  That said, I am
> currently testing my theory, so I won't promise anything, either. :)
Please do give us an update when you get any progress:)

> 
> Thanks,
> -Toshi
> 
>