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

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Message-id: <4E7C39FB.3050707@huawei.com>
Date:	Fri, 23 Sep 2011 15:49:15 +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 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

> Bjorn
>
> [1] http://www.dig64.org/home/DIG64_HPPF_R1_0.pdf
>
>>> ---
>>>   drivers/acpi/processor_driver.c |    6 ++++++
>>>   1 files changed, 6 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/acpi/processor_driver.c
>>> b/drivers/acpi/processor_driver.c
>>> index a4e0f1b..03d92d6 100644
>>> --- a/drivers/acpi/processor_driver.c
>>> +++ b/drivers/acpi/processor_driver.c
>>> @@ -641,6 +641,7 @@ static void acpi_processor_hotplug_notify(acpi_handle
>>> handle,
>>>         struct acpi_processor *pr;
>>>         struct acpi_device *device = NULL;
>>>         int result;
>>> +       u32 id;
>>>
>>>
>>>         switch (event) {
>>> @@ -677,6 +678,11 @@ static void acpi_processor_hotplug_notify(acpi_handle
>>> handle,
>>>                                     "Driver data is NULL, dropping EJECT\n");
>>>                         return;
>>>                 }
>>> +               id = pr->id;
>>> +               if (acpi_bus_trim(device, 1)) {
>>> +                       printk(KERN_ERR  PREFIX
>>> +                                   "Fail to Remove CPU %d\n", id);
>>> +               }
>>>                 break;
>>>         default:
>>>                 ACPI_DEBUG_PRINT((ACPI_DB_INFO,
>>> --
>>> 1.7.6.0
>>>
>>>
>>
>
> .
>


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