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    SubjectRe: Problems with SMP & ACPI powering off
    Rafael J. Wysocki wrote:
    > On Friday, 28 September 2007 06:57, Len Brown wrote:
    >> On Thursday 27 September 2007 18:00, Rafael J. Wysocki wrote:
    >>> On Thursday, 27 September 2007 23:29, Mark Lord wrote:
    >>>> Question: do we disable all CPUs except 0 when doing ACPI power off?
    >>> No, but we should.
    >> We used to.
    >> It is absolutely mandatory -- else it confuses the BIOS on some boards
    >> b/c it isn't expecting SMM to get entered from other than cpu0.
    >
    > Can we use the CPU hotplug for that, like in the suspend/hibernation case?

    Well, so far it's working: about ten poweroffs since I patched it,
    and no issues with any of them. Prior to that, it seemed like about
    one in five poweroffs wouldn't (power off).

    It'll take a lot more testing to confirm, though.

    What can I call to determine if more than one CPU is enabled, anyway?

    Here's the hack I'm using here, very situation (2 cores) specific,
    and it still has some printk's leftover with a sleep so I have time
    to read them before the lights go out. :)

    --- old/arch/i386/kernel/reboot.c 2007-09-27 17:17:00.000000000 -0400
    +++ linux/arch/i386/kernel/reboot.c 2007-09-27 17:15:35.000000000 -0400
    @@ -393,8 +393,22 @@
    .halt = native_machine_halt,
    };

    +static void kill_cpu1(void)
    +{
    + extern int cpu_down(unsigned int cpu);
    +
    + printk(KERN_EMERG "kill_cpu1: was running on CPU%d\n", smp_processor_id());
    + /* Some bioses don't like being called from CPU != 0 */
    + set_cpus_allowed(current, cpumask_of_cpu(0));
    + printk(KERN_EMERG "kill_cpu1: now running on CPU%d\n", smp_processor_id());
    + cpu_down(1);
    + printk(KERN_EMERG "kill_cpu1: done\n");
    + msleep(1000);
    +}
    +
    void machine_power_off(void)
    {
    + (void)kill_cpu1();
    machine_ops.power_off();
    }

    -
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