linux-kernel - Re: [PATCH v5] acpi: Fix CPU hot removal problem

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Date:	Thu, 29 Sep 2011 11:41:35 +0800
From:	"canquan.shen" <shencanquan@...wei.com>
To:	Chen Gong <gong.chen@...ux.intel.com>
Cc:	len.brown@...el.com, Bjorn Helgaas <bhelgaas@...gle.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 v5] acpi: Fix CPU hot removal problem

On 2011/9/29 11:14, Chen Gong wrote:
> 于 2011/9/24 14:10, canquan.shen 写道:
>> 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
>> did't go to really remove cpu in the cpu removal code path.
>>
>> This patch adds acpi_bus_hot_remove_device 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>
>> ---
>> drivers/acpi/processor_driver.c | 13 +------------
>> drivers/acpi/scan.c | 4 ++--
>> include/acpi/acpi_bus.h | 1 +
>> 3 files changed, 4 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/acpi/processor_driver.c
>> b/drivers/acpi/processor_driver.c
>> index a4e0f1b..8429688 100644
>> --- a/drivers/acpi/processor_driver.c
>> +++ b/drivers/acpi/processor_driver.c
>> @@ -665,18 +665,7 @@ static void
>> acpi_processor_hotplug_notify(acpi_handle handle,
>> case ACPI_NOTIFY_EJECT_REQUEST:
>> ACPI_DEBUG_PRINT((ACPI_DB_INFO,
>> "received ACPI_NOTIFY_EJECT_REQUEST\n"));
>> -
>> - if (acpi_bus_get_device(handle, &device)) {
>> - printk(KERN_ERR PREFIX
>> - "Device don't exist, dropping EJECT\n");
>> - break;
>> - }
>> - pr = acpi_driver_data(device);
>> - if (!pr) {
>> - printk(KERN_ERR PREFIX
>> - "Driver data is NULL, dropping EJECT\n");
>> - return;
>> - }
>> + acpi_bus_hot_remove_device(handle);
>
> As the description in __acpi_os_execute(in acpi_os_hotplug_execute),
> /*
> * We can't run hotplug code in keventd_wq/kacpid_wq/kacpid_notify_wq
> * because the hotplug code may call driver .remove() functions,
> * which invoke flush_scheduled_work/acpi_os_wait_events_complete
> * to flush these workqueues.
> */
> If so, why not using following call:
>
> acpi_os_hotplug_execute(acpi_bus_hot_remove_device, acpi_device->handle);
>
>

It is ok if using the acpi_os_hotplug_execute. but it is complex and 
more time for removal cpu because it is add to queue and some time the 
work will be called.
I think that it is clear to call directly acpi_bus_hot_remove_device 
function in acpi_processor_hotplug_notify.


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