On Thu, 2011-09-22 at 10:53 -0600, Bjorn Helgaas wrote: > On Wed, Sep 14, 2011 at 8:56 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: > > On Wed, Sep 14, 2011 at 7:06 PM, canquan.shen <shencanquan@xxxxxxxxxx> 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@xxxxxxxxxx> > > > > Reviewed-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > 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? I have been looking at this code and I have been thinking along the same lines. Using acpi_bus_trim() to remove CPU does not power down the CPU and allow firmware to deconfigure it. Calling acpi_bus_hot_remove_device() is a better approach. While we are at it, we should also fix the conditional in acpi_bus_hot_remove_device() after executing _EJ0 to make sure we do not print warning if _EJ0 is not supported by firmware: --- scan.c.orig 2011-09-22 11:14:52.801074429 -0600 +++ scan.c 2011-09-22 11:15:24.061699647 -0600 @@ -129,7 +129,7 @@ static void acpi_bus_hot_remove_device(v * TBD: _EJD support. */ status = acpi_evaluate_object(handle, "_EJ0", &arg_list, NULL); - if (ACPI_FAILURE(status)) + if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) printk(KERN_WARNING PREFIX "Eject device failed\n"); -- Khalid > 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 > >> > >> > > -- ==================================================================== Khalid Aziz Server Solutions Technology Lab (970)898-9214 Hewlett-Packard khalid.aziz@xxxxxx Fort Collins, CO -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
