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

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Message-ID: <1354814926.21116.17.camel@misato.fc.hp.com>
Date:	Thu, 06 Dec 2012 10:28:46 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Jiang Liu <liuj97@...il.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 Fri, 2012-12-07 at 01:30 +0800, Jiang Liu wrote:
> 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:)

Yes, will do.

Thanks,
-Toshi


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