linux-kernel - Re: [PATCH v4] acpi: Fix CPU hot removal problem

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Message-id: <4E7D223C.1040809@huawei.com>
Date:	Sat, 24 Sep 2011 08:20:12 +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>, linqiangmin@...wei.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	khalid.aziz@...com
Subject: Re: [PATCH v4] acpi: Fix CPU hot removal problem

On 2011/9/23 22:16, Bjorn Helgaas wrote:
> On Fri, Sep 23, 2011 at 1:49 AM, canquan.shen<shencanquan@...wei.com>  wrote:
>> On 2011/9/23 0:53, Bjorn Helgaas wrote:
>>>
>>> On Wed, Sep 14, 2011 at 8:56 PM, Bjorn Helgaas<bhelgaas@...gle.com>
>>>   wrote:
>>>>
>>>> On Wed, Sep 14, 2011 at 7:06 PM, canquan.shen<shencanquan@...wei.com>
>>>>   wrote:
>>>>>
>>>>> We run linux as a guest in Xen environment. When we used the xen tools
>>>>> (xm vcpu-set<n>) to hot add and remove vcpu to and from the guest, we
>>>>> encountered the failure on vcpu removal. We found the reason is that it
>>>>> didn't go to really remove cpu in the cpu removal code path.
>>>>>
>>>>> This patch adds acpi_bus_trim in acpi_process_hotplug_notify to fix this
>>>>> issue. With this patch, it works fine for us.
>>>>>
>>>>> Signed-off-by:Canquan Shen<shencanquan@...wei.com>
>>>>
>>>> Reviewed-by: Bjorn Helgaas<bhelgaas@...gle.com>
>>>
>>> On second thought, let's think about this a bit more.
>>>
>>> As I mentioned before, I have a long-term goal to move the hotplug
>>> flow out of drivers and into the ACPI core.  That will be easier if
>>> the code in the drivers is as generic as possible.
>>>
>>> The dock and acpiphp hot-remove code calls acpi_bus_trim(), then
>>> evaluates _EJ0.  The core acpi_bus_hot_remove_device() function
>>> already does both acpi_bus_trim() and _EJ0.  This function is
>>> currently only used when we write to sysfs "eject" files, but I wonder
>>> if we should use it in acpi_processor_hotplug_notify() as well.
>>>
>>> That would get us one step closer to removing this gunk from the
>>> drivers and having acpi_bus_notify() look something like this:
>>>
>>>      case ACPI_NOTIFY_EJECT_REQUEST:
>>>          driver->ops.remove(device);
>>>          acpi_bus_hot_remove_device(device);
>>>          break;
>>>
>>> There is a description of a CPU hot-remove that does include _EJ0
>>> methods in the "DIG64 Hot-Plug&    Partitioning Flows Specification"
>>> [1], sec 2.2.4.  I know this document is Itanium-oriented, but this
>>> part seems fairly generic and it's the only description of the process
>>> I've seen so far.
>>>
>>> So would using acpi_bus_hot_remove_device() instead of acpi_bus_trim()
>>> also solve your problem, Canquan?
>>>
>> Yes. It can solve my problem.
>> I fully aggree to replace acpi_bus_hot_remove_device() to acpi_bus_trim().
>> Initially I insert the acpi_bus_hot_remove_device() in acpi_bus_notify
>> function . lately I think I should give a chance for user,and so send
>>   KOBJ_OFFLINE message to the udvev module.
>>
>> But why add the  driver->ops.remove(device) before
>> acpi_bus_hot_remove_device(device).  it can be called in
>> acpi_bus_hot_remove_device code path as bellowing:
>>     acpi_bus_trim
>>         acpi_bus_remove
>>             device_release_driver
>>                 __device_release_driver
>>                         acpi_device_remove
>>                                 acpi_drv->ops.remove
>
> OK.  Maybe the future acpi_bus_notify() code would be even simpler.
> The point is that the ACPI core should handle the notification, call
> the driver's .remove() method, and do whatever namespace cleanup is
> required (i.e., acpi_bus_trim()).  None of this should be in the
> driver itself.
>
> Can you re-post your patch, using acpi_bus_hot_remove_device() instead
> of acpi_bus_trim()?  Please include Khalid's tweak, too, so we don't
> print warnings for CPUs that don't supply _EJ0 methods.
>
> Bjorn
>
> .
>
OK. I will modify it and re-post the patch which will include Khalid's 
tweak.  and Thank Khalid for attention this patch.

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