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SubjectRe: [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@google.com> wrote:
>> On Wed, Sep 14, 2011 at 7:06 PM, canquan.shen<shencanquan@huawei.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@huawei.com>
>>
>> Reviewed-by: Bjorn Helgaas<bhelgaas@google.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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