linux-kernel - Re: Re : [PATCH] acpi: Fix hot cpu remove problem on acpi subsystem

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Date:	Thu, 08 Sep 2011 08:21:09 +0800
From:	"canquan.shen" <shencanquan@...wei.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	len.brown@...el.com,
	"shemminger@...tta.com" <shemminger@...tta.com>,
	"yakui.zhao@...el.com" <yakui.zhao@...el.com>,
	"xiaowei.yang@...wei.com" <xiaowei.yang@...wei.com>,
	hanweidong <hanweidong@...wei.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	linqiangmin@...wei.com, james.chenjiabo@...wei.com
Subject: Re: Re : [PATCH] acpi: Fix hot cpu remove problem on acpi subsystem

On 2011/9/7 14:57, Bjorn Helgaas wrote:
> On Tue, Sep 6, 2011 at 7:40 PM, canquan.shen<shencanquan@...wei.com>  wrote:
>> On 2011/9/7 2:38, Bjorn Helgaas wrote:
>
>>> Is acpi_processor_remove() called when you remove a processor?  I see
>>> a path where it will be called via acpi_eject_store():
>>>
>>>      acpi_eject_store
>>>        acpi_os_hotplug_execute(acpi_bus_hot_remove_device)
>>>        acpi_bus_hot_remove_device
>>>          acpi_bus_trim
>>>            acpi_bus_remove
>>>              device_release_driver
>>>                dev->driver->remove (acpi_processor_remove())
>>>              acpi_device_unregister
>>>                device_unregister
>>>                  device_del
>>>                    kobject_uevent(KOBJ_REMOVE)
>>>
>>> but as far as I can tell, this path is only used when we write
>>> something to the "eject" sysfs file.  I would think we'd want to use
>>> most of this same path when we hot remove a CPU via the ACPI SCI
>>> mechanism.
>>>
>>
>> Because in my patch will send the KOBJ_REMOVE event to udev module. and I
>> write a udev rule like the following:
>> ACTION=="remove",DRIVER=="processor",SUBSYSTEM=="acpi",RUN+="/bin/bash -c
>> 'echo 1>  /sys%p/eject'"
>> This rule will write "1" to the "eject" sysfs file. and then call
>> acpi_eject_store function.
>
> Hmmm.  I think I understand your proposal, but it seems like a
> convoluted path to me.
>
> I guess the real question is whether we must give userspace a chance
> to decide whether to actually do the remove or not.  Is there a
> requirement to do that?  Neither the dynamic device removal flow (ACPI
> spec 4.0a, sec 6.3) nor the ejection flow example (fig 6-5) mentions
> doing that.
>
    I think we should give userspace a chance to decide whether do  the 
remove or not. About the cpu remove, it has two part, one in the linux 
kernel which mainly online/offline cpu, another is acpi core driver, 
which mainly add and remove the device of processor.
    giving userspace a chance is not acpi spec requirement. but it is 
flexible for linux kernel. many driver use the udev mechanism to has a 
chance for user to decide how to handle the event of kernel.

> I mentioned before that I think the ACPI hotplug code should be ripped
> out of the drivers and consolidated in the ACPI core.  I think it's
> pretty clear from the spec that the 0-0x7f notifications (Bus Check,
> Device Check, Eject Request, etc.) are designed to be handled by the
> core, not by individual drivers.  We handle hotplug in the drivers
> today, but I think that's mainly because we never implemented support
> in the Linux ACPI core.  There are comments in acpi_bus_check_device()
> and acpi_bus_check_scope() about what we *should* be doing there.
>
> I am opposed to adding more hotplug support to individual drivers
> because I still hope that someday we'll support it in the ACPI core.
> Many ACPI drivers don't support hotplug at all, and the ones that do
> support hotplug do it in a variety of ways.  It's all quite a mess.
>
> Bjorn
>
> .
>

I admit it is convoluted path for hot cpu remove. and the acpi processor 
driver will be consolidated in the acip core. but how to do in the acpi 
core ? I think it maybe directly call acpi_bus_hot_remove_device or send 
KOBJ_OFFLINE event to linux kernel.

I will modify the processor driver by add the acpi_bus_trim function in 
acpi_processor_hotplug_notify. and create the patch for fix this problem.
Could you help me to merge to latest linux kernel? Thanks for your 
answer again.

---
canquan.shen





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