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

[Toshi Kani <toshi.kani@hp.com>]

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. :)

Thanks,
-Toshi


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