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    SubjectRe: [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<> wrote:
    >> On 2011/9/23 0:53, Bjorn Helgaas wrote:
    >>> On Wed, Sep 14, 2011 at 8:56 PM, Bjorn Helgaas<>
    >>> wrote:
    >>>> On Wed, Sep 14, 2011 at 7:06 PM, canquan.shen<>
    >>>> 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<>
    >>>> Reviewed-by: Bjorn Helgaas<>
    >>> 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:
    >>> 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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